Anatomy of the Cat

by Jacob Reighard; H. S. Jennings

III. MUSCLES OF THE BODY.

1. Muscles of the Back.

A. Muscles of the Shoulder

(connecting the forelimb with the back) ([Fig. 68]).

M. trapezius.—The trapezius muscle is divided in the cat into three portions, the spinotrapezius, the acromiotrapezius, and the clavotrapezius.

M. spinotrapezius, or trapezius inferior ([Fig. 68], j).—The spinotrapezius (caudal part of the human trapezius) is a flat triangular muscle.

Origin from the tips of the spinous processes of all or nearly all the thoracic vertebræ and from the intervening supraspinous ligament. The origin may extend from a point anywhere between the first and fourth spines to any point between the eleventh and thirteenth.

Insertion along an S-shaped line ([Fig. 76], k-l) which crosses the tuberosity of the scapular spine and forms an angle with the spine of about forty-five degrees. The line extends on one side onto the fascia covering the supraspinatus muscle, and on the other side onto the fascia covering the infraspinatus, but does not reach the borders of the scapula. The cranial two-thirds of the insertion is by a flat tendon which is broader craniad.

Relations.—Outer surface with the cutaneus maximus, and craniad with the acromiotrapezius (h). Inner surface with the latissimus dorsi (m) caudad and with the rhomboideus, supraspinatus, and infraspinatus craniad. Caudal border free; cranial border in contact with the acromiotrapezius (h).

Action.—Draws the scapula dorsocaudad.

M. acromiotrapezius, or trapezius superior ([Fig. 68], h).—The acromiotrapezius (middle part of the human trapezius) is a flat four-sided muscle just craniad of the spinotrapezius, from the median dorsal line to the scapular spine.

Origin along the median dorsal line from the spinous process of the axis to a point anywhere between the spinous processes of the first and fourth thoracic vertebræ. Its caudal two-thirds is from a flat tendon which is directly continuous with the muscle of the opposite side and thus bridges the depression between the vertebral borders of the scapulæ. This tendon narrows craniad, and its cranial fourth is attached by a fascia to the spinous processes of the cervical vertebræ. At the cranial border of the muscle the fibres sometimes reach the middle line. The fibres of the muscle run nearly transversely.

Insertion ([Fig. 76], h).—Into the outer surface of the metacromion, the glenoid border of the scapular spine from the metacromion to the tuberosity, and along a line continued for about one centimeter from the tuberosity onto the surface of the spinotrapezius (j) at the junction of its muscular and tendinous portions.

[Fig. 68].—First Layer of Body-muscles, beneath the Skin and Skin-muscles.

a, M. frontoscutularis; b, M. masseter; c, M. sternomastoideus; d, M. clavotrapezius; e, M. clavobrachialis; f, M. levator scapulæ ventralis; g, M. acromiodeltoideus; h, M. acromiotrapezius; i, M. spinodeltoideus; j, M. spinotrapezius; k, caput longum of M. triceps brachii; l, caput laterale of M. triceps brachii; m, M. latissimus dorsi; n, M. xiphihumeralis; o, M. pectoralis minor; p, M. obliquus abdominis externus; q, M. sartorius; r, M. tensor fasciæ latæ; s, M. caudofemoralis; t, M. biceps femoris; u, M. semitendinosus; v, M. extensor caudæ lateralis; w, M. abductor caudæ externus; x, M. flexor caudæ longus; y, lumbodorsal fascia, superficial layer; z, fascia lata. 1, parotid gland; 2, submaxillary gland.

Relations.—Outer surface with the cutaneus maximus, the integument and platysma. Inner surface with a mass of fat partially covering the rhomboideus; with the occipitoscapularis, spinotrapezius, supraspinatus, levator scapulæ, and splenius. Near its origin its caudal border touches the outer surface of the spinotrapezius (j). Its cranial border is overlaid near its insertion by the levator scapulæ ventralis (f) and is closely related to the caudal border of the clavotrapezius (d) near its origin.

Action.—The two muscles hold the scapulæ together.

M. clavotrapezius ([Fig. 68], d).—The clavotrapezius (cranial part of the human trapezius) is a flat muscle passing from the lambdoidal crest and middorsal line to the clavicle and covering the side of the neck.

Origin.—The medial half of the lambdoidal crest and the middorsal line between the crest and the caudal end of the spine of the axis. The fibres are parallel and pass caudoventrad so that the muscle covers the ventral surface of the neck caudally and fills the concavity at the front of the shoulder.

Insertion into the clavicle and into a raphe between the clavotrapezius and the clavobrachial (e) muscles. This raphe extends along the clavicle and for some distance laterad of it. The muscle is partly continuous with the clavobrachial (e).

Relations.—Outer surface with the platysma, and at its craniomedial angle with the levator auris longus. Inner surface with the rhomboideus, splenius, occipitoscapularis, levator scapulæ, cleidomastoid, and supraspinatus. The cranial edge touches the sternomastoid. The caudal border touches the acromiotrapezius near the origin.

Action.—Draws the scapula craniodorsad.

This muscle and the clavobrachial (e) are sometimes considered as forming a single muscle, the cephalohumeral, or cephalobrachial.

M. occipitoscapularis (or levator scapulæ dorsalis or rhomboideus capitis) ([Fig. 73], a).—The occipitoscapularis (equivalent to a part of the human rhomboideus) is a slender flat muscle from the lambdoidal ridge to the coracovertebral angle of the scapula.

Origin, the medial half of the lambdoidal ridge beneath the clavotrapezius ([Fig. 68], d). The origin does not extend quite to the middle line. The muscle passes almost directly caudad. Its caudal end is thicker and narrower than the cranial end and is wedged between the rhomboideus dorsally and the levator scapulæ ventrally.

Insertion either into the inner surface of the levator scapulæ near its dorsocranial border at its insertion or into the scapula near the coracovertebral angle ([Fig. 78], f) or into both. Its fibres are very closely related to those of the rhomboideus.

Relations.—By its outer surface with the clavotrapezius ([Fig. 68], d) and acromiotrapezius (h). At its insertion it is often overlaid by either the rhomboideus or the levator scapulæ or both. By its inner surface with the splenius ([Fig. 73], b). Its caudal third is wedged between the rhomboideus and the levator scapulæ.

Action.—Draws forward and rotates the scapula.

M. rhomboideus (probably equivalent to the human rhomboideus major and rhomboideus minor).—A rather thick trapezoid muscle connecting the vertebral border of the scapula with the spinous processes of the adjacent vertebræ.

Origin from the caudal two or three fifths of the cervical supraspinous ligament and from the sides and tips of the first four thoracic vertebral spines and the interspinous ligaments caudad of these four spines. It passes lateroventrad, and the fibres converge somewhat so that the line of insertion is shorter than the line of origin.

Insertion by a short tendon (1 millimeter long) into the vertebral border of the scapula, the line of insertion passing gradually from the inner ([Fig. 78], e) to the outer ([Fig. 76], i) surface; and by fleshy fibres into the outer surface of the glenovertebral angle of the scapula ([Fig. 76], i) in close connection with the origin of the teres major (j). A bundle of fibres at the cranial border may be inserted into the cranial border of the levator scapulæ at its insertion.

Relations.—By its outer surface with the spinotrapezius ([Fig. 68], j), acromiotrapezius (h), latissimus dorsi (m), and clavotrapezius (d); it is usually partially separated from these muscles by a mass of fat. By its inner surface near its insertion with the serratus anterior ([Fig. 73], i) and levator scapulæ ([Fig. 73], h), and craniad with the splenius ([Fig. 73], b), and the tendon of the serratus posterior superior ([Fig. 73], l). At its lateral end it touches the occipitoscapularis ([Fig. 73], a), serratus anterior (i), levator scapulæ (h), supraspinatus ([Fig. 75], a), and infraspinatus ([Fig. 75], c), and the teres major ([Fig. 75], d).

Action.—Draws the scapula toward the vertebral column.

M. cleidomastoideus (clavicular portion of the human sternocleidomastoid) ([Fig. 65], h).—A narrow flat muscle between the mastoid process and the clavicle.

Origin from the apex and caudal margin of the mastoid process of the temporal bone, by tendon and muscle fibres. The muscle passes caudad, becoming broader and thinner.

Insertion into the lateral four-fifths of the clavicle within the insertion of the clavotrapezius, and into the raphe which continues laterad of the clavicle.

Relations.—Outer or lateral surface at the caudal end with the clavotrapezius ([Fig. 65], j); further craniad with the depressor conchæ ([Fig. 64], b), the platysma, and the sternomastoid ([Fig. 65], g). Inner or medial surface with the supraspinatus ([Fig. 75], a) caudad, with the mass of fat in the axilla at its middle, with the levator claviculæ ventralis ([Fig. 65], i) and obliquus capitis superior ([Fig. 71], e) craniad.

Action.—Pulls the clavicle craniad when the head is fixed. Turns the head and depresses the snout when the clavicle is fixed.

M. levator scapulæ ventralis, or levator claviculæ ([Fig. 68], f; [Fig. 65], i; [Fig. 72], c, c′, c″) (not usually found in man).

Origin ([Fig. 72], c′, c″) in two parts. (1) By fleshy fibres from the ventral surface of the atlantal transverse process near its caudal border (c′). (2) By a small tendon from the ventral surface of the basioccipital opposite the middle of the length of the bulla tympani (c″) in common with the longus capitis (a). The two heads unite to form a flat band which passes caudoventrad and is inserted ([Fig. 76], f) by a flat short tendon, about eight millimeters broad, into the outer surface of the metacromion along its ventral border, and into the infraspinatus fossa for one or two millimeters distad of that border.

Relations.—Near the insertion the dorsal border overlaps the border of the acromiotrapezius ([Fig. 68], h), and the ventral border is attached by strong fascia to the border of the clavotrapezius ([Fig. 68], d). The outer surface is in relation with the longissimus capitis ([Fig. 73], g), clavotrapezius ([Fig. 68], d), cleidomastoid ([Fig. 73], d), platysma, and the skin. The inner surface is in relation caudad with the supraspinatus and with a mass of fat and a lymphatic gland which occupy the hollow of the shoulder. Craniad it is in relation with the cleidomastoid ([Fig. 73], d), the scalenus ([Fig. 73], f), the longus capitis ([Fig. 73], e), and the obliquus superior ([Fig. 71], e).

Action.—Pulls the scapula craniad.

M. latissimus dorsi ([Fig. 68], m; [Fig. 65], q; [Fig. 77], e).—A large triangular sheet covering rather more than the dorsocranial half of the abdomen and thorax. It arises from the middorsal line, from the pelvis to the fifth thoracic spine, and is inserted into the humerus.

Origin from the tips of the neural spines of the vertebræ from the fourth or fifth thoracic to about the sixth lumbar. As far as the tenth or eleventh thoracic vertebra the origin is directly by muscle-fibres. Caudad of this is a broad triangular tendon which may be so closely united to the tendons of the underlying muscles that it cannot be separated. The muscle passes cranioventrad, the fibres converging to the axilla. In the axilla a part of the cutaneus maximus and the epitrochlearis ([Fig. 65], r) take origin from the outer surface.

Insertion.—The muscle then ends in a flat tendon, to the cranial surface of which the fibres of the teres major ([Fig. 77], c) are attached. Five to ten millimeters from the humerus the muscle-fibres of the teres give place to the tendon-fibres, and the conjoined tendon of the teres and latissimus which is thus formed ([Fig. 79], d′) is inserted into a rough elongated area ([Fig. 82], f) which lies parallel with the pectoral ridge on the medial surface of the shaft of the humerus ([Fig. 48], g). The teres tendon forms the proximal part of the conjoined tendon. A part of the tendon of the latissimus may join the pectoralis minor at its distal or caudal border ([Fig. 65]), and thus it may contribute to the formation of both pillars of the bicipital arch ([Fig. 65], t′).

Relations.—Its outer surface is covered caudad by the cutaneus maximus, and craniad by the spinotrapezius ([Fig. 68], j) and the long head of the triceps ([Fig. 68], k). The cranial border comes into relation with the spinotrapezius (j) and teres major ([Fig. 77], c). The caudal border is in contact at the ventral end with the xiphihumeralis ([Fig. 65], p) and pectoralis minor ([Fig. 65], o). The inner surface of the latissimus covers near its cranioventral end parts of the xiphihumeralis ([Fig. 68], n), pectoralis minor ([Fig. 68], o), teres major ([Fig. 77], c), and serratus anterior ([Fig. 73], i). The caudal border covers a portion of the obliquus externus abdominis ([Fig. 68], p); the dorsal and middle portions cover parts of the longissimus dorsi ([Fig. 69], f″), the spinalis dorsi ([Fig. 69], g), the serratus posterior superior ([Fig. 73], l), and serratus posterior inferior ([Fig. 73], n).

Action.—Pulls the arm caudodorsad.

M. serratus anterior and levator scapulæ ([Fig. 73], i and h) in the cat are continuous at both origin and insertion, and it is barely possible to separate their contiguous borders without cutting the fibres. The muscle extends from the transverse processes of the last five cervical vertebræ and from the first nine or ten ribs to the medial surface of the scapula near its vertebral margin ([Fig. 78], c and d).

M. serratus anterior (or serratus magnus) ([Fig. 73], i).

Origin.—From the first nine or ten ribs in as many subdivisions. The first subdivision arises from the whole or nearly the whole of the caudal border of the first rib. The next four or five arise either from the ribs or from the costal cartilages near or at their junction with the ribs. The last four subdivisions arise from the ribs at increasing distances from the cartilages. The fibres converge and the subdivisions join one another.

Insertion ([Fig. 78], c) into a narrow area on the medial surface of the scapula near the vertebral border. The glenoid half of the insertion is by a short tendon, the remainder by muscle-fibres.

Relations.—Outer (lateral) surface with the latissimus dorsi ([Fig. 68], m), teres major ([Fig. 77], c), subscapularis ([Fig. 77], a), and near the origin with the rectus abdominis ([Fig. 73], k), the scalenus ([Fig. 73], f-f‴), and the obliquus externus ([Fig. 68], p). Inner (medial) surface with the serratus posterior superior ([Fig. 73], l) and its tendon, and with the intercostales externi ([Fig. 73], m). At its insertion the muscle touches the rhomboideus. The cranial edge is united to the caudal edge of the levator scapulæ ([Fig. 73], h).

Action.—Depressor of the scapula.

M. levator scapulæ ([Fig. 73], h).

Origin.—From the dorsal tubercles of the transverse processes of the last five cervical vertebræ and from the ligaments between the tubercles. A slip sometimes arises from the atlas.

Insertion ([Fig. 78], d) into a triangular area on the medial surface of the scapula near its vertebral border. It is continuous with the insertion of the serratus anterior.

Relations.—Outer (lateral) surface with a mass of fat separating it from the clavotrapezius ([Fig. 68], d) and cleidomastoid ([Fig. 65], h), and with the subscapularis ([Fig. 77], a). Inner (medial) surface with the splenius ([Fig. 73], b), the tendon of the serratus posterior superior ([Fig. 73], l), and the cervical portion of the longissimus dorsi ([Fig. 69], f″). Near the insertion the muscle touches the occipitoscapularis ([Fig. 73], a) and rhomboideus. Caudal border united with the serratus anterior ([Fig. 73], i).

Action.—Draws the scapula cranioventrad.

B. Muscles of the Back

(interconnecting parts of the vertebral column) ([Fig. 69]).—The muscles connected with the vertebral column form a mass which is less markedly differentiated into distinct muscles than is the case in the limbs. A great longitudinal mass of fibres begins in the sacral region and extends along the vertebral column to the head. This mass contains fibres running in various directions and attached at one or both ends to the sacrum, the innominate bones, the spinous, transverse, and articular processes, and to the arches, of the vertebræ; to the ribs and to the head, and having in general the function of moving the vertebræ in various ways, or of moving parts connected with the vertebræ. In some regions, especially the cervical, it is possible to distinguish clearly distinct muscles which have been differentiated from this mass. In the greater part of its extent, however, it is possible to distinguish only more or less closely interconnected bundles,—the more clearly marked of which have received special names.

The great dorsal mass running along each side of the vertebral column, occupying the space between the spinous processes and the transverse processes, receives the general name of M. extensor dorsi communis; the separate muscles are to be considered as parts or differentiations of this. The largest part of the mass is in the lumbar region (first portion of the longissimus dorsi, [Fig. 69], f). At the caudal end of the thorax a lateral mass, parts of which become connected with the ribs, is separated off from the main part of the muscle; this extends craniad into the cervical region as M. iliocostalis (h). The main portion of the longissimus dorsi (f′) continues craniad on the medial side of the iliocostal into the neck region. At about the level of the eighth or ninth thoracic vertebra a strip begins to become separated off on the medial side of the longissimus; further forward it becomes clearly distinct, forming the spinalis dorsi (g). The separate muscles connecting the cervical vertebræ with each other and with the head are differentiations of the extensor dorsi communis.

A still deeper set of fibres, interconnecting the vertebræ, forms the multifidus spinæ and a number of other small muscles.

A description of the different bundles of fibres, under the names usually given, follows. Certain general principles are observed in some of the names used. Muscles which interconnect the spinous processes of the vertebræ receive the name spinalis. Those interconnecting contiguous spinous processes are called interspinalis. Muscles attached at one end to transverse processes, at the other to the spinous processes, receive the name transversospinalis. Semispinalis has the same signification as transversospinalis, but is a name usually applied to subdivisions of the transversospinalis group. The intertransversarii are muscles interconnecting the transverse processes.

[Fig. 69].—Deep Muscles of Body, Exposed after Removal of the Muscles shown in [Fig. 73].

a, M. biventer cervicis; b, M. complexus; c, M. obliquus capitis superior; d, M. longus atlantis; e, cut end of M. longissimus capitis; f, f′, f″, M. longissimus dorsi; g, M. spinalis dorsi; h, M. iliocostalis; i, Mm. intercostales externi; k, Mm. intercostales interni; l, M. transversus abdominis.

(a) Muscles of the Lumbar and Thoracic Regions.

—The muscles of the lumbar and thoracic regions are mostly covered by a strong fascia, known as the lumbodorsal fascia ([Fig. 68], y). This consists of two sheets, the superficial sheet being applied directly to the outer surface of the inner sheet, or separated from it by a mass of fat.

The superficial sheet ([Fig. 68], y) overlies the lumbar region and the caudal half of the thoracic region. On the medial side it is attached to the spinous processes of the vertebræ and is united closely to the deeper layer. Laterally this fascia is continuous with the latissimus dorsi (m) and obliquus abdominis externus (p). Caudad it is attached to the spine of the ilium and becomes continuous with the fascia covering the gluteus muscles.

The deeper sheet ([Fig. 70], c) is of a tendinous character, forming the external tendinous layer of the longissimus dorsi, many of whose fibres take origin from its under surface. It is [described] more fully in the account of this muscle.

M. longissimus dorsi ([Fig. 69], f, f′, f″; [Fig. 70], a and b).—A very large muscle, filling most of the region between the spinous processes and transverse processes of the lumbar and thoracic vertebræ, and extending into the cervical region.

The muscle is largest in the lumbar region ([Fig. 69], f; [Fig. 70]), where it is divided into a narrow medial ([Fig. 70], a) and a thick lateral portion ([Fig. 70], b), the latter being again partially subdivided by the fascia. The two parts unite farther craniad.

The medial division ([Fig. 70], a) consists of muscular bundles connecting the spinous processes of the vertebræ with the accessory and mammillary processes of other vertebræ; it is continuous caudad with the extensor caudæ lateralis ([Fig. 70], f). The muscle-fibres take origin in the sacral region by small round tendons from the spinous processes of the last two sacral and the caudal vertebræ. They curve cranioventrad, forming a large belly, and are inserted into the accessory and mammillary processes of the lumbar vertebræ. In the thoracic region this division unites with that portion of the lateral division in which the fibres coming from the fascia of origin are inserted into the laminæ and transverse processes of the thoracic vertebræ.

The lateral division ([Fig. 70], b) is much larger than the medial one, forming in the lumbar region a nearly cylindrical mass.

[Fig. 70].—Muscles on the Dorsal Side of the Vertebral Column in the Lumbar, Sacral, and Caudal Regions.

Both sheets of the lumbodorsal fascia have been removed, the deep layer (c) being cut where it passes into the longissimus dorsi. 1, crest of ilium; 4-7, tips of spinous processes of the fourth to seventh lumbar vertebræ. I, II, tips of spinous processes of first two sacral vertebræ. a, b, M. longissimi dorsi (a, medial portion; b, lateral portion; b′, portion taking origin from the lumbodorsal fascia); c, cut edge of deep layer of lumbodorsal fascia; d, M. multifidus spinæ; e, M. extensor caudæ medialis; f, M. extensor caudæ lateralis, g, M. abductor caudæ externus.

Origin from the crest of the ilium ([Fig. 70], 1) and the medial surface of the ilium as far caudad as the auricular impression; also from the deep layer of the lumbodorsal fascia (c). This fascia is connected with the crest of the ilium and with the tips of the spinous processes of the vertebræ in the lumbar and thoracic regions, and from it a large proportion of the fibres of the longissimus take origin. In the lumbar region it dips into the muscle as an intermediate longitudinal sheet (c), partially dividing it lengthwise into two parts. Fibres taking origin from the lateral surface of this intermediate sheet curve cranioventrad, and are inserted on the transverse processes of the lumbar vertebræ. Fibres taking origin from the medial surface of the sheet pass mediocraniad and are inserted into the accessory processes and the surfaces of the vertebral arches. In the thoracic region ([Fig. 69], f′) most of the fibres are inserted in separate bundles by small tendons on the transverse processes of the vertebræ, while some of the medial fibres unite with tendinous strands which become attached to the laminæ and articular processes of the vertebræ. At the region of the eighth or ninth thoracic vertebra the spinalis dorsi ([Fig. 69], g) begins to be separated off on the medial side, the separation becoming complete only some distance farther craniad; the longissimus dorsi then continues into the cervical region (f″). Bundles of fibres become attached in the manner above described to transverse processes of all the thoracic vertebræ. In the cervical region (f″) the muscle spreads out and becomes thinner, and bundles of fibres become attached to the transverse processes of the cervical vertebræ as far forward as the second. In the more cranial portion of its extent the muscle receives fibres having origin on the articular processes and laminæ of the cervical and a few of the more cranial thoracic vertebræ.

The portion of the muscle which is inserted on the cervical transverse processes (f″) is sometimes distinguished as the longissimus cervicis; it is not well separated from the rest of the muscle in the cat. The longissimus capitis ([Fig. 69], c; [Fig. 73], g) is to be considered a differentiated cranial portion of this muscle.

Relations.—Outer surface with the following, beginning with the caudal end: the sartorius ([Fig. 68], q), the latissimus dorsi ([Fig. 68], m), the lumbodorsal fascia ([Fig. 68], y), the serratus posterior inferior ([Fig. 73], n) and superior ([Fig. 73], l), and the levator scapulæ ([Fig. 73], h). Lateral margin with the abdominal muscles, the iliocostal ([Fig. 69], h), and the levator scapulæ ([Fig. 73], h). Medial side with the multifidus spinæ ([Fig. 70], d), the spinous processes of the thoracic vertebræ, the spinalis dorsi ([Fig. 69], g), the complexus ([Fig. 69], b), the biventer cervicis ([Fig. 69], a), and the longissimus capitis ([Fig. 69], e).

Action.—Extends the vertebral column.

M. iliocostalis ([Fig. 69], h).—This is a muscle about 1½ to 2 centimeters wide, lying on the dorsal portion of the ribs, laterad of the longissimus dorsi (f′). It is composed of many partly separated bundles, each with an oblique tendon. The muscle begins at the last or next to the last rib, where it is connected with the longissimus by a rather small bundle of fibres. The rest of the muscle-fibres take origin in bundles from the lateral surface of the ribs, at about the angles, or from thin tendons connecting the angles, of the ribs; they pass obliquely craniad and are inserted, usually by tendons, on the lateral surface of the third or fourth rib craniad of the one on which the given bundle has origin. The insertions on any given rib lie ventrad of the origins on the same rib. In the cat this muscle is confined to the thoracic region.

Relations.—Outer surface with the serratus posterior inferior ([Fig. 73], n) and superior ([Fig. 73], l), and the levator scapulæ ([Fig. 73], h). Inner surface with the dorsal surface of the ribs, the external intercostals ([Fig. 69], i), and craniad with the levatores costarum. Medial edge in contact with the longissimus dorsi ([Fig. 69], f′).

Action.—Draws the ribs together.

M. spinalis dorsi ([Fig. 69], g).—A muscle interconnecting the spinous processes of vertebræ some distance apart, in the thoracic and cervical regions. It lies on the medial side of the longissimus dorsi (f′).

Origin by strong tendons from the tips of the spinous processes of the tenth to the thirteenth thoracic vertebræ. These tendons represent the cranial portion of the deep layer of the lumbodorsal fascia, and give origin also to many fibres of the longissimus dorsi, so that the two muscles are completely united at the origin of the spinalis. They become separated at about the level of the sixth thoracic vertebra, the spinalis forming a strong separate bundle passing into the neck region close against the sides of the spinous processes. The insertion is by fleshy bundles into the sides of the spinous processes of the first nine or ten thoracic vertebræ and of the cervical vertebræ as far forward as the second. Some of the fibres of this muscle pass craniad into the biventer cervicis ([Fig. 69], a).

Relations.—Outer surface with the tendons of the serratus posterior inferior ([Fig. 73], n) and serratus posterior superior ([Fig. 73], l), and with the splenius ([Fig. 73], b), biventer cervicis ([Fig. 69], a), and complexus ([Fig. 69], b). Lateral and ventral surface with the longissimus dorsi (f′); medial surface with the spinous processes and the multifidus spinæ.

Action.—Extensor of the vertebral column.

M. multifidus spinæ.—This consists of bundles of fibres which have origin on the transverse processes or neighboring parts, pass craniodorsad across one or more vertebræ, and are inserted into the spinous processes of vertebræ lying some distance craniad of the origin. They lie deeper than the muscles previously described. The muscle is most strongly developed in the lumbar region ([Fig. 70], d), where it forms a thick interwoven mass in which it is difficult to distinguish separate bundles. The fibres in this region have origin on the accessory or mammillary processes and usually pass over more than one vertebra between origin and insertion; their insertions reach the dorsal ends of the spinous processes, so that part of the muscle lies immediately beneath the lumbar fascia. In other regions the multifidus is covered by other muscles. In the thoracic region the separate bands are more distinct, and usually pass in their course over but one intervening vertebra. In the cervical region the bands are interconnected, forming a fairly distinct single muscle, which is [described] separately below as the semispinalis cervicis ([Fig. 71], c). The portion of this muscle attached to the head (semispinalis capitis) forms the biventer cervicis ([Fig. 69], a) and complexus (b). Caudad this muscle passes onto the tail as the extensor caudæ medialis ([Fig. 70], c).

Relations.—Outer and lateral surface in the lumbar region with the longissimus dorsi ([Fig. 69], f) and the lumbodorsal fascia ([Fig. 68], y); in the thoracic region with the longissimus dorsi ([Fig. 69], f′) and spinalis dorsi (g). Inner surface with the arches, articular processes, and spinous processes of the vertebræ.

Action.—Extends the back when the muscles of both sides work together. Turns the vertebral column obliquely sideways when one set acts alone.

The deepest layer of the multifidus forms what is sometimes distinguished as the Mm. rotatores; no separate layer of this sort is to be made out in the cat.

Mm. interspinales.—Muscle-bundles passing from the spinous process of one vertebra to that of the vertebra immediately craniad or caudad of it. They are best developed in the lumbar region.

Mm. intertransversarii.—Muscle-fibres interconnecting the transverse processes. In the lumbar region the intertransversarii mediales connect the accessory and mammillary processes; the intertransversarii laterales lying between the transverse processes. In other regions only one set of the intertransversarii is to be distinguished.

(b) Dorsal Muscles of the Cervical Region.

—The clavotrapezius ([Fig. 68], d) and occipitoscapularis ([Fig. 73], a) have been described in connection with the muscles of the [shoulder]. The remaining muscles of this region may be considered as differentiations of the general vertebral musculature (M. extensor dorsi communis).

M. splenius ([Fig. 73], b.)—A large sheet of muscle covering the dorsal part of the side of the neck, beneath the trapezii.

Origin from the whole cervical ligament and from the fascia covering the deeper muscles along a line which extends from the first thoracic spinous process caudolaterad for about two centimeters.

Insertion by a thin tendon into the whole lambdoidal ridge. Laterad the tendon may be fused with that of the longissimus capitis ([Fig. 73], g).

Relations.—Outer surface with the sternomastoid ([Fig. 68], c), occipitoscapularis ([Fig. 73], a), clavotrapezius ([Fig. 68], d), rhomboideus, tendon of the serratus posterior superior ([Fig. 73], l), and the levator scapulæ ([Fig. 73], h). Lateral edge closely united with the longissimus capitis ([Fig. 73], g). Inner surface with the longissimus capitis, complexus ([Fig. 69], b), and biventer cervicis ([Fig. 69], a).

Action.—Lateral flexor of the head. The two together elevate the head.

M. longissimus capitis (trachelomastoideus) ([Fig. 73], g; [Fig. 69], e).—This is a slender muscle lying close against the lateral border of the splenius ([Fig. 73], b), and sometimes fused with the splenius at its craniad end. It is a cranial continuation of the longissimus dorsi ([Fig. 69], f″).

Origin by five slips which are attached by strong tendons to the anterior articular processes of the last four cervical vertebræ. The tendons are common to this muscle and the complexus. The five slips unite to form a flat belly which has its

Insertion by a strong rounded tendon into the mastoid process of the temporal bone. The tendon may be closely united to that of the splenius.

Relations.—Lateral surface with the sternomastoid ([Fig. 68], c), the levator scapulæ ([Fig. 73], h), and longissimus dorsi ([Fig. 69], f″). Medial surface with the splenius ([Fig. 73], b) (to which it is partly united), the complexus ([Fig. 69], b), and the longus atlantis ([Fig. 69], d).

Action.—Lateral flexor of the head.

M. biventer cervicis ([Fig. 69], a) (medial portion of M. semispinalis cervicis et capitis).—The biventer cervicis is a flat muscle which lies beneath the splenius ([Fig. 73], b), next the median line of the neck, with its fibres longitudinal.

Origin in three or four slips from the surface of the three or four aponeurotic arches which take origin from the tips of the spinous processes of the last cervical and the first three thoracic vertebræ and pass laterad and caudad to the anterior processes of the second, third, fourth, and fifth thoracic vertebræ. These arches are deviated from their straight course by four aponeurotic bands which pass from them obliquely caudad and dorsad to the sides of the spinous processes of the vertebræ into which the arches are inserted. The arches form the beginning of the sheet of fascia which passes outside of the longitudinal supraspinous muscles, and the anchoring bands form the beginning of a similar sheet which passes within the longitudinal supraspinous muscles. An additional slip may take origin from the cervical ligament between the last cervical and the first thoracic vertebræ. The fibres form a flat band divided by two or three oblique tendinous intersections. It adheres closely to the cervical supraspinous ligament.

Insertion by a strong tendon into the medial part of the lambdoidal crest.

Relations.—Outer surface with the splenius ([Fig. 73], b) and at the caudal end with the longissimus dorsi ([Fig. 69], f″). Inner surface with the spinalis dorsi ([Fig. 69], g), the semispinalis cervicis ([Fig. 71], c), and the rectus capitis posterior major ([Fig. 71], a). Medial edge with the muscle of the opposite side; lateral edge with the complexus ([Fig. 69], b).

Action.—Raises the snout.

M. complexus ([Fig. 69], b) (lateral portion of M. semispinalis cervicis et capitis).—The complexus is closely associated with the biventer cervicis (a) and lies on its lateral side beneath the splenius ([Fig. 73], b).

Origin by tendinous bands from the anterior articular processes of the last five or six cervical and the first one, two, or three thoracic vertebræ. The same bands give origin externally to the fibres of the longissimus capitis ([Fig. 69], e), and internally to those of deeper muscles of the neck. The six or more muscular slips continued from these tendons unite to form a flat band, the

Insertion of which is by a flat tendon into the medial third of the lambdoidal crest some distance ventrad of the free edge of the crest. Near the insertion the lateral border of the muscle is connected by an aponeurotic band to the lateral border of the transverse process of the atlas.

Relations.—Outer surface at the dorsal border with the biventer cervicis ([Fig. 69], a); at the middle with the splenius ([Fig. 73], b); at the ventral border with the longissimus capitis ([Fig. 69], e) and the longissimus dorsi ([Fig. 69], f″). Inner surface with the cervical portion of the spinalis dorsi, with the semispinalis cervicis ([Fig. 71], c), the obliquus capitis inferior ([Fig. 71], b), the rectus capitis posterior major ([Fig. 71], a), and the obliquus superior ([Fig. 71], e).

Action.—Raises the head.

M. spinalis dorsi extends into the cervical region; it has been [described].

M. semispinalis cervicis ([Fig. 71], c).—This represents that portion of the multifidus spinæ which extends into the cervical region. It is not composed of distinct bundles, like the multifidus of the thoracic region, but all the fibres are united into a fairly well-defined muscle.

Origin from the articular processes of the last five cervical vertebræ.

Insertion into the spinous processes of the cervical vertebræ up to the second, the largest part of the muscle being inserted into the caudal end of the spine of the atlas.

Relations.—Outer surface with the spinalis dorsi ([Fig. 69], g) and the complexus ([Fig. 69], b). Inner surface with the vertebræ.

Action.—Extends the neck.

M. longissimus dorsi extends into the cervical region, where it is often distinguished as the longissimus cervicis ([Fig. 69], f″). It has been [described].

M. longus atlantis ([Fig. 71], f; [Fig. 69], d).—This represents a differentiated portion of the longissimus dorsi.

Origin from the transverse process and the side of the vertebral arch of the third cervical vertebra.

Insertion into the caudolateral angle of the wing of the atlas.

Relations.—Dorsal surface with the complexus ([Fig. 69], b), the longissimus capitis ([Fig. 69], e), and the obliquus inferior ([Fig. 71], b). Ventral surface with the scalenus ([Fig. 71], g), longissimus dorsi ([Fig. 69], f″), and levator scapulæ ([Fig. 71], h).

Action.—Extends the neck and turns the head sideways.

M. rectus capitis posterior major ([Fig. 71], a).

Origin.—The whole length of the spinous process (or crest) of the axis, or its caudal part only. It is united by a raphe to the opposite muscle. The muscle passes craniad and laterad to its

Insertion into an area ventrad of the medial part of the lambdoidal crest beneath the insertion of the complexus ([Fig. 69], b) and the biventer cervicis ([Fig. 69], a).

Relations.—Dorsal surface with the biventer cervicis ([Fig. 69], a). Ventral surface with the rectus capitis posterior medius ([Fig. 71], d) and the obliquus capitis inferior.

Action.—Raises the snout.

M. rectus capitis posterior medius ([Fig. 71], d). (This is in man a part of the rectus capitis posterior major.)—It lies beneath the rectus capitis posterior major ([Fig. 71], a).

[Fig. 71].—Deep Muscles of the Neck, after the Removal of Mm. Biventer Cervicis and Complexus.

a, M. rectus capitis posterior major; b, M. obliquus capitis inferior; c, M. semispinalis cervicis; d, M. rectus capitis posterior medius; e, M. obliquus capitis superior; f, M. longus atlantis; g, M. scalenus (part of cervical portion); h, cut end of M. levator scapulæ.

Origin from the cranial end of the axial spine. It forms a triangular prismatic mass which passes craniad and has its

Insertion into an elongated area on the occipital bone, ventrad of the median half of the lambdoidal crest.

Relations.—Dorsal surface with the rectus capitis posterior major ([Fig. 71], a). Ventral surface with the atlas and the rectus capitis posterior minor.

Action.—Assists the rectus capitis posterior major.

M. rectus capitis posterior minor.—A small triangular muscle beneath the rectus capitis posterior medius ([Fig. 71], d).

Origin by the apex of the triangle from the cranial border of the dorsal arch of the atlas for about two millimeters laterad of the median line. The muscle passes over the ligament which connects the atlas to the occiput and adheres to it.

Insertion into an elongated area on the occipital bone, ventrad of the insertion of the rectus capitis posterior medius for about five millimeters next to the median line.

Relations.—Dorsal surface with the rectus capitis posterior medius. Ventral surface with the posterior atlanto-occipital membrane.

Action.—Assists the rectus capitis posterior major.

M. obliquus inferior ([Fig. 71], b).

Origin from the whole lateral surface of the spine of the axis. The parallel fibres form a thick mass which passes laterad and craniad.

Insertion into the dorsal surface of the transverse process of the atlas along a narrow area near its lateral margin.

Relations.—Outer surface with the rectus capitis posterior major ([Fig. 71], a), the complexus ([Fig. 69], b), and the obliquus superior ([Fig. 71], e). Inner surface with the axis.

Action.—Rotates the head.

M. obliquus capitis superior ([Fig. 71], e; [Fig. 72], e).—This is a triangular muscle passing from the outer border of the atlas laterad of the recti capitis posteriores to the occiput.

Origin from the lateral border of the transverse process of the atlas on its ventral margin. The fibres pass craniad and diverge.

Insertion into the caudal side of the mastoid process of the temporal bone and into a line parallel with the lambdoidal ridge and ventrad of it, from the mastoid process to within one centimeter of the median line.

Relations.—Outer surface with the splenius ([Fig. 73], b), complexus ([Fig. 69], b), and longissimus capitis ([Fig. 73], g). Inner surface with the obliquus inferior ([Fig. 71], b), the wing of the atlas, and the rectus lateralis ([Fig. 72], d). Ventral border with the cleidomastoid ([Fig. 73], d) and one head of the levator scapulæ ventralis ([Fig. 72], c′).

Action.—Flexes the head laterally.

Mm. interspinales and intertransversarii are found in the neck region also; they are described with the muscles of the [back].

C. Muscles of the Tail.

—M. extensor caudæ medialis ([Fig. 70], e).—This is a continuation caudad of the multifidus spinæ ([Fig. 70], d); it lies next to the dorsal median line, the muscles of right and left side touching one another in the middle line.

Origin by numerous fleshy bundles from the spinous processes of the sacral and first caudal vertebræ. The fibres pass caudad and are inserted by tendons into the articular processes and the dorsal surface of the caudal vertebræ.

Action.—Extends (raises) the tail.

M. extensor caudæ lateralis ([Fig. 70], f).—This is a continuation caudad of the medial portion of the longissimus dorsi ([Fig. 70], a); it lies just laterad of the extensor caudæ medialis ([Fig. 70], e).

Origin in many fleshy bundles from the articular processes of the sacral vertebræ, and the transverse processes of the caudal vertebræ. The fibres curve dorsocaudad and are inserted by many long slender tendons on the dorsal surfaces of the caudal vertebræ. The muscle grows continually smaller as it passes caudad.

Action.—Raises the tail.

M. abductor caudæ (coccygis) externus ([Fig. 68], w; [Fig. 70], g).—A rounded muscle on the lateral surface of the cranial part of the tail.

Origin from the medial side of the dorsal border of the ilium, and from the dorsal surface of the sacrum. The muscle passes caudad, lying just ventrad of the extensor lateralis, and is inserted into the transverse processes and lateral surfaces of the caudal vertebræ, as far back as the eighth or ninth.

Action.—Bends the tail sideways.

M. abductor caudæ internus (or M. coccygeus).—A large flat muscle, having origin on the spine of the ischium. The muscle passes dorsomediad, spreading out, and is inserted into the transverse processes of the second to the fourth caudal vertebræ.

Relations.—Lateral surface with the caudofemoralis ([Fig. 68], s), gluteus maximus, and pyriformis. Medial surface with the iliocaudalis and the flexor caudæ longus ([Fig. 68], x).

M. iliocaudalis (Str.-D.) ([Fig. 162], 11′, [page 398]).—This represents a portion of the levator ani of man, and in some specimens is united with that muscle ([Fig. 162], 11) in the cat.

Origin along the ventral half of the medial surface of the ilium, caudad of the sacrum. The fibres pass caudad and are inserted by a flat tendon into the ventral surface of the caudal vertebræ, from the second or third to about the seventh.

Relations.—Lateral surface with the gluteus maximus and abductor caudæ internus ([Fig. 68], w). Medial surface with the levator ani ([Fig. 162], 11), with which this muscle may be partly united.

Action.—The two muscles together flex the tail.

M. flexor caudæ longus ([Fig. 162], 12; [Fig. 113], c, [page 270]).

Origin on the ventral surface of the last lumbar vertebra, of the sacrum, and of the transverse processes of the caudal vertebræ. Caudad the muscle forms long, strong tendons which are inserted on the ventral surface of the tail.

Relations.—Lateral surface with the ilium, the gluteus maximus, the abductor caudæ internus, the iliocaudalis, and the skin of the tail. Dorsally it touches in the caudal region the abductor caudæ externus ([Fig. 68], w), medially the flexor caudæ brevis ([Fig. 162], 13).

Action.—Flexes the tail.

M. flexor caudæ brevis ([Fig. 162], 13).

Origin on the ventral surface of the caudal vertebræ, from the first to the seventh or eighth. The principal head comes from the first vertebra. The bundles thus formed pass caudad and are inserted each into the ventral surface of a vertebra some distance caudad of the origin. The muscle extends to about the tenth caudal vertebra, and its most caudal parts are closely interconnected with the flexor caudæ longus.

Relations.—Lateral edge with the flexor caudæ longus. Medial edge in the sacral region with the levator ani ([Fig. 162], 11) and the iliocaudalis ([Fig. 162], 11′); in the caudal region with the muscle of the opposite side.

Action.—Flexes the tail.

2. Muscles on the Ventral Side of the Vertebral Column.

A. Lumbar and Thoracic Regions.

—The iliopsoas ([Fig. 162], 8) belongs in this group, but since it moves the leg it is [described] with the muscles of the pelvic limbs.

M. psoas minor ([Fig. 162], 9, [page 398]).—This muscle lies along the ventral surface of the vertebral column, next to the peritoneum, and extends from the thoracic vertebræ to the ilium.

Origin usually by five heads, from the caudal border of the centra of the last two (or one) thoracic and first three (or four) lumbar vertebræ. These heads also serve as origin for a part of the iliopsoas, and are closely united at their origin with the quadratus lumborum. They unite to form an, at first, rather large flat muscle, which rapidly becomes smaller caudad, finally forming a slender tendon which is inserted on the iliopectineal line, just craniad of the acetabulum.

Relations.—Dorsolateral surface with the quadratus lumborum and iliopsoas ([Fig. 162], 8). Ventral surface with the pleura and diaphragm near the origin; with the peritoneum caudad.

Action.—Flexes the back in the lumbar region.

M. quadratus lumborum.—A flat muscle lying on the ventral surface of the transverse processes of the lumbar vertebræ. Craniad it has origin on the ventral surface of the last two thoracic vertebræ, and by a few fibres from the last rib. The muscle passes caudad, lying on the lateral side of the psoas minor ([Fig. 162], 9), and becomes attached to each of the transverse processes of the lumbar vertebræ. Caudad the muscle passes into a strong flat tendon which is inserted into the anterior inferior spine of the ilium.

Relations.—Dorsal surface with the transverse processes and the intertransverse muscles. Ventral and medial surfaces with the psoas minor ([Fig. 162], 9) and iliopsoas ([Fig. 162], 8).

Action.—Bends the vertebral column sideways.

B. Muscles on the Ventral Side of the Neck

([Fig. 65], [page 109]).—M. sternomastoideus ([Fig. 65], g; [Fig. 68], c).—The sternomastoid (sternal portion of the human sternocleidomastoid) is a flat band one to three centimeters wide extending from the cranial end of the manubrium and the midventral line craniad of it to the lambdoidal ridge.

The origin extends from the cranial end of the manubrium along the midventral line as far as the caudal border of the cricoid cartilage, and is in two parts. The caudal portion arises from the lateral surface of the manubrium along the dorsal half of its cranial end, and from the median raphe for about one centimeter craniad of the manubrium. Its fibres are parallel and tend to diverge into two layers. The cranial portion arises by means of fibres which cover the median line and interdigitate with the fibres of the opposite muscle between the cricoid cartilage and a point a few millimeters craniad of the manubrium. Its caudal border is thus overlaid by the caudal portion. Its fibres converge and join those of the caudal portion. The muscle passes dorsocraniad and is

Inserted by means of a flat tendon into the lateral half of the lambdoidal ridge and into a continuation of the ridge onto the mastoid portion of the temporal bone as far as the mastoid process. The thickest part of the tendon is inserted into the mastoid process.

Relations.—Outer surface at the caudal end with the pectoralis major ([Fig. 65], l); in the middle part with the platysma, the depressor conchæ ([Fig. 64], b), and with the external jugular vein ([Fig. 65], 5), which crosses it obliquely; at the cranial end with the submaxillary ([Fig. 65], 2) and parotid (1) glands. Inner surface with the sternohyoid ([Fig. 65], e), sternothyroid (g′), internal jugular vein, longus capitis muscle, the cleidomastoid (h), levator scapulæ ventralis (i), a large lymphatic gland ventrad of the ear, and the splenius ([Fig. 73], b).

Action.—One muscle turns the head and depresses the snout. Both together depress the snout.

M. sternohyoideus ([Fig. 65], e).—A slender muscle on the midventral line of the neck close to the opposite muscle.

Origin from the cranial border of the first costal cartilage. The muscle passes craniad closely united near its caudal end to the sternothyroid (g′).

Insertion ([Fig. 67], m) into the outer half of the ventral surface of the body of the hyoid bone caudad of the origin of the geniohyoid ([Fig. 67], g).

Relations.—Outer surface with the sternomastoid ([Fig. 65], g). Inner surface with the thyrohyoid ([Fig. 65], f; [Fig. 67], p), the trachea ([Fig. 67], 4), and the larynx.

Action.—Draws the hyoid caudad. Raises the ribs and sternum when the hyoid is fixed.

M. sternothyreoideus ([Fig. 65], g′).—The sternothyroid lies beneath the sternohyoid and is connected with it at its caudal end.

Origin from the first costal cartilage beneath the sternohyoid.

Insertion ([Fig. 67], o) into the lateral part of the caudal border of the thyroid cartilage of the larynx.

Relations.—Outer surface with the sternohyoid ([Fig. 65], e) and laterally with the sternomastoid ([Fig. 65], g). Inner surface with the trachea ([Fig. 67], 4), and at the lateral edge with the thyroid gland ([Fig. 67], 6).

Action.—Pulls the larynx caudad.

M. scalenus ([Fig. 73], f-f‴).—This is a large and complex muscle lying on the ventral side of the neck and the lateral surface of the thorax. It might equally well be classified with the muscles of the thorax. It is divisible into a considerable number of interconnected bundles which are sometimes described as separate muscles.

The largest, middle portion (scalenus medius) (f′) takes origin by thin tendons from the sixth, seventh, eighth, and ninth ribs, just dorsad of their junction with the cartilages; these tendons unite near their origins to form a flat band which becomes fleshy at about the fifth rib, passes craniad, and unites just craniad of the first rib with the other parts of the muscle. The dorsal portion (scalenus posterior) (f″) has origin by a very slender tendon from about the middle of the outer surface of the third or fourth rib; it extends craniad as a narrow band which passes laterad between the heads of the serratus anterior (i) that are attached to the second and third (or third and fourth) ribs, and unites with the other heads. The ventral head (part of scalenus anterior) (f‴) arises by one or two minute tendons from the cartilages of the second and third ribs; they are partly united with the transversus costarum (j). This ventral head passes craniad and unites with the other heads.

These three divisions unite just craniad of the first rib with each other and with the cervical portion of the muscle (f) (part of scalenus anterior). This consists of a number of small bundles of fibres which arise from the first rib and the transverse processes of the first thoracic and the last six cervical vertebræ.

The insertion is onto the transverse processes of all the cervical vertebræ, including the axis and atlas. According to Strauss-Durckheim the fibres from any given transverse process are inserted into the transverse processes of all the vertebræ craniad of it.

The muscle is partly continuous craniad with the longus capitis (e). The cervical nerves pass out between the bundles of the cervical portion.

Relations.—Outer (lateral) surface in the thoracic region with the external oblique ([Fig. 68], p), the pectoralis minor ([Fig. 65], o), and in part with the serratus anterior ([Fig. 73], i); in the cervical region with the sternomastoid ([Fig. 65], g). Inner (medial) surface with the serratus anterior ([Fig. 73], i), the levator scapulæ ([Fig. 73], h), the longus atlantis, the transverse processes of the cervical vertebræ, and the longus capitis ([Fig. 73], e).

Action.—Flexes the neck and draws the ribs craniad.

M. longus capitis (or rectus capitis anterior major) ([Fig. 72], a; [Fig. 73], e).—This is a long muscle lying on the ventral aspect of the cervical vertebræ. With the muscle of the opposite side and the underlying longus colli ([Fig. 72], g′) it forms a trough in which lie the œsophagus, pharynx, and trachea.

Origin by five (or six) heads from the ventral margins of the transverse processes of the cervical vertebræ from the second to the sixth inclusive. The heads unite into a common belly, the lateral border of which is united with the levator scapulæ ventralis ([Fig. 72], c) near its insertion.

Insertion into the body of the sphenoid bone between the bulla and the middle line. The insertion extends craniad onto the basisphenoid.

Relations.—Ventral surface with the sternomastoid ([Fig. 65], g) and the large lymphatic gland ventrad of the external ear. Lateral surface with the scalenus ([Fig. 72], h) and craniad with the levator scapulæ ventralis ([Fig. 72], c-c″). Medial surface with the carotid artery, the trachea, œsophagus, and pharynx. Dorsal edge with the vertebræ, the longus colli ([Fig. 72], g′), and the rectus capitis anterior minor ([Fig. 72], b).

Action.—Lowers the snout.

M. rectus capitis anterior minor ([Fig. 72], b).—This is a flat band beneath (dorsad of) the longus capitis (a).

Origin from the ventral surface of the inferior arch (body) of the atlas (3) for about five millimeters laterad of the middle line.

Insertion into a deep depression on the basioccipital caudad of the insertion of the longus capitis (a) and between the caudal end of the bulla (1) and the median line.

Relations.—Ventral surface with the longus capitis (a). Dorsal surface with the anterior (ventral) atlanto-occipital membrane (2).

Action.—Depresses the snout.

[Fig. 72].—Muscles on the Ventral Surface of the Cervical Vertebræ.

On the left side the longus capitis and one head of the levator scapulæ ventralis have been cut, in order to show the rectus capitis anterior minor. a, M. longus capitis; b, M. rectus capitis anterior minor; c, M. levator scapulæ ventralis (c′, its atlantal head; c″, its occipital head); d, M. rectus capitis lateralis; e, M. obliquus capitis superior; f, M. longissimus capitis; g, M. longus colli (g′, its cervical portion; g″, its thoracic portion); h, part of M. scalenus. 1, bulla tympani; 2, ventral atlanto-occipital membrane; 3, ventral arch of atlas; 4, first rib.

M. rectus capitis lateralis ([Fig. 72], d).—This lies ventrad of the obliquus superior (e) on the ventral face of the transverse process of the atlas and at first appears to be a part of the obliquus superior.

Origin from the median half of the ventral surface of the transverse process of the atlas. The fibres form a cylindrical mass which passes craniad and slightly laterad.

Insertion into the fossa laterad of the condyle of the occipital bone.

Relations.—Ventral surface with the digastric ([Fig. 65], b) and the lymphatic gland ventrad of the ear. Dorsal surface with the wing of the atlas.

Action.—Flexes the head laterally.

M. longus colli ([Fig. 65], g′, g″).—A long, rather slender muscle lying on the ventral surface of the cervical and first six thoracic vertebræ. It consists of many separate bundles, and is divisible into a thoracic and a cervical portion.

The thoracic portion (g″) has origin by six heads from the ventral surface of the first six thoracic vertebræ. The separate heads join to form a band which passes craniad and is inserted for the most part into the processus costarius of the sixth cervical vertebra; a portion of it joins the cervical division of the muscle.

The cervical portion (g′) is a continuation craniad of the thoracic portion. It arises in small bundles from the transverse processes and sides of the ventral surfaces of the centra of the cervical vertebræ. These bundles pass craniomediad, so that those from the muscles of opposite sides meet and are inserted on the centra of the vertebræ in the middle line, each pair of bundles forming a V opening caudad. The most cranial insertion is into the tubercle on the middle of the ventral surface of the ventral arch of the atlas (3).

Relations.—Dorsal surface with the centra of the vertebræ. Ventral surface in the thorax with the trachea; in the neck with the œsophagus. Medial edge with the muscle of the opposite side. Lateral margin in the cervical region with the longus capitis (a).

Action.—Bends the neck.

3. Muscles of the Thorax.

A. Breast-muscles (connecting the arm and thorax)

([Fig. 65], [page 109]).

The muscles connecting the arm with the sternum, corresponding to the pectoralis muscles of man, fall into a considerable number of not always clearly separated bundles in the cat. We shall distinguish by name four such bundles; these might be, and frequently are, further subdivided.

M. pectoantibrachialis ([Fig. 65], m).—This is a small flat bundle about one or two centimeters wide, forming the most superficial portion of the pectoralis group.

Origin on the lateral surface of the manubrium. The muscle passes laterad onto the arm and is inserted by a flat tendon into the superficial fascia of the dorsal border of the forearm, near the elbow-joint. The tendon is continuous craniad with the border of the clavobrachial (k), so that a bundle of fibres may pass from this muscle to be inserted with the clavobrachial, or a bundle from the clavobrachial to be inserted with this. The tendon is continuous caudad with that of the epitrochlearis (r). The fascia of insertion may be traced to an attachment into the dorsal border of the ulna. This muscle usually receives near its insertion a slip, sometimes called its caudal division, from the deep layer of the pectoralis major.

Relations.—Outer surface with the integument. Inner surface with both divisions of the pectoralis major (l) on its medial two-thirds, and with the biceps (t) and bicipital arch (t′) in its lateral one-third. The cranial border is closely applied to that of the clavobrachial (k), except at the two ends.

Action.—Draws the arm mediad.

M. pectoralis major, or ectopectoralis ([Fig. 65], l, l′).—In this it is usually possible to distinguish a superficial and a deep layer.

The superficial (l′) layer is a flat band of fibres one or two centimeters wide.

Origin from a raphe in the midventral line, along the cranial half of the manubrium and for five to ten millimeters craniad of it.

Insertion ([Fig. 81], f).—The pectoral ridge of the middle third of the shaft of the humerus, slightly dorsad of the line of insertion of the deep portion.

Relations.—Outer surface with the clavobrachial ([Fig. 65], k) and integument, the medial end caudally with the pectoantibrachialis (m), and the distal end with the brachialis (v). Inner surface with the deep portion (l), the fibres of which it crosses obliquely.

The deep portion (l) is a flat band of parallel fibres about three times as broad as the superficial portion.

Origin.—The ventral surface of the manubrium and of the first three divisions of the sternum, and the median raphe for about one centimeter craniad of the manubrium. It passes directly laterad.

Insertion ([Fig. 81], e) along a line which begins at the infraspinatus fossa of the great tuberosity, and runs parallel to the deltoid ridge until it reaches the pectoral ridge at the junction of the second and third fourths of the humerus and then continues in the direction of the pectoral ridge as far as the junction of the third and fourth fourths of the humerus. Some of its fibres may pass caudad of the biceps and be inserted with the epitrochlearis. Into the part of the line which is parallel to the deltoid ridge the muscle is inserted by a flat tendon; into the remainder of the line it is usually inserted directly by muscle-fibres, though at its caudal end its insertion may again be tendinous.

Relations.—Outer surface with the cutaneus maximus, the outer layer of the pectoralis major ([Fig. 65], l′), the pectoantibrachialis (m), and the clavobrachial (k). Inner surface with the pectoralis minor (o), the proximal end of the humerus, the coracobrachialis ([Fig. 77], f), and the supraspinatus ([Fig. 77], d) at the insertion of the latter. At the cranial part of its origin it touches the sternomastoid ([Fig. 65], g) and sternohyoid ([Fig. 65], e).

Action.—Draws the arm mediad and turns the foot forward.

M. pectoralis minor, or entopectoralis ([Fig. 65], o).—This is a fan-shaped mass of fibres, flat but thicker than the pectoralis major.

Origin from the lateral half of the first six divisions of the body of the sternum and sometimes from the xiphoid process. The fibres are divisible into several bundles which vary in extent and distinctness and are sometimes described as separate muscles. They pass craniolaterad and converge so that the line of insertion is about one-half as long as that of the origin.

Insertion ([Fig. 81], d) into the humerus along a line which forms the ventral border of the bicipital groove at the proximal end of the bone, passes thence onto the pectoral ridge and continues in the direction of the pectoral ridge nearly as far as the middle of the length of the humerus. The cranial and caudal fibres are inserted by means of a thin tendon; the middle fibres directly. The cranial border of the tendon of insertion is continued as a thin tendon to the coracoid process; it is closely united with the insertion of the supraspinatus.

Relations.—By its outer surface with the pectoralis major ([Fig. 65], l) over its cranial half; with the cutaneus maximus, latissimus dorsi ([Fig. 65], q), and integument over its caudal half. By its inner surface with the xiphihumeralis ([Fig. 65], p), rectus abdominis ([Fig. 73], k), and a mass of fat in the axilla. The tendon of the xiphihumeralis is also connected with its inner surface near its insertion. Its cranial border is free. Its caudal border is in relation at its medial end with the xiphihumeralis, at its lateral end with the tendon of the latissimus dorsi ([Fig. 65], q).

Action.—Draws the arm toward the middle line.

M. xiphihumeralis ([Fig. 65], q).—A long, thin, narrow muscle which may be considered as part of the pectoralis minor.

Origin a median raphe along the xiphoid process or at an angle to the median line on the rectus abdominis muscle. It passes craniad, becoming gradually smaller, and about two centimeters from its insertion ends in a thin tendon.

Insertion.—It ends in a flat tendon which in passing is connected by a strong fascia with the tendon of the latissimus ([Fig. 65], q). It passes along the inner surface of the pectoralis minor (o) to be inserted with its cranial fibres near the ventral border of the bicipital groove.

Relations.—Outer surface with the cutaneus maximus at its medial end, with the pectoralis minor (o) at its distal end. Inner surface with the external oblique ([Fig. 68], p), the rectus abdominis ([Fig. 73], k), and a mass of fat in the axilla. Borders free. Some of the fibres of the cutaneus maximus are attached to its outer surface.

Action.—Assists the pectoralis minor.

B. Muscles of the Wall of the Thorax.

—M. serratus posterior superior ([Fig. 73], l).—A thin sheet of muscle and tendon beneath the serratus anterior (i) on the dorsal part of the thorax and neck.

Origin by fleshy slips from the outer surfaces of the first nine ribs just ventrad of their angles. The origin may extend as far as the tenth or eleventh ribs. The first slip is usually delicate. The fibres are directed dorsad and craniad and unite to form a continuous sheet. This ends along a longitudinal line opposite the vertebral transverse processes in the aponeurosis which covers the longissimus dorsi and other muscles in this region. Its insertion is into the median dorsal raphe between the axial spinous process and the tenth thoracic spinous process.

Relations.—Outer surface with the serratus anterior (i), the latissimus dorsi ([Fig. 68], m), and the rhomboideus. Inner surface with the external intercostals ([Fig. 73], m), the iliocostal ([Fig. 69], h), the longissimus dorsi ([Fig. 69], f), the spinalis dorsi ([Fig. 69], g), and the splenius ([Fig. 73], b).

Action.—Draws the ribs craniad.

M. serratus posterior inferior ([Fig. 73], n).—The serratus posterior inferior is a thin muscle lying caudad of the serratus posterior superior (l) and sometimes overlying the caudal end of the latter.

Origin by four or five heads from the last four or five ribs. In some specimens only three heads may be present. The separate bundles pass dorsocaudad and unite to form a continuous sheet which ends in a continuation of the aponeurosis of the serratus posterior superior (l).

Insertion into the lumbar spinous processes and the intervening interspinous ligaments.

Relations.—Outer surface with the latissimus dorsi ([Fig. 68], p), and at the origins with the intercostales externi ([Fig. 73], m). Inner surface with the intercostales interni ([Fig. 69], k) at the origin and with the intercostales externi ([Fig. 69], i), iliocostal ([Fig. 69], h), longissimus dorsi ([Fig. 69], f), and the caudal end of the spinalis dorsi ([Fig. 69], g).

[Fig. 73].—Body Muscles exposed after Removal of the Forelimb and the Muscles shown in [Fig. 68].

a, M. occipitoscapularis (cut); b, M. splenius; c, M. levator scapulæ ventralis (cut); d, M. cleidomastoideus (cut); e, M. longus capitis; f, M. scalenus (f′, middle division; f″, dorsal division; f‴, ventral division; f, cervical portion); g, M. longissimus capitis; h, M. levator scapulæ (cut); i, M. serratus anterior (cut); j, M. transversus costarum; k, M. rectus abdominis (k′, its tendon); l, M. serratus posterior superior; m, M. intercostales externi; n, M. serratus posterior inferior; o, M. obliquus abdominis internus; p, lumbodorsal fascia.

Action.—Assists the serratus posterior superior.

M. transversus costarum, or sternocostalis externus ([Fig. 73], j).—This is a thin muscle applied to the cranial part of the side of the thorax, covering the cranial end of the rectus abdominis (k).

Origin by tendon from the side of the sternum between the attachments of the third and sixth ribs. The muscle passes dorsocraniad to its

Insertion on the first rib and the lateral portion of its costal cartilage.

Relations.—Outer surface with the pectoralis minor ([Fig. 65], o). Inner surface with the scalenus ([Fig. 73], f‴), the rectus abdominis ([Fig. 73], k), and the intercostales externi ([Fig. 73], m). At its insertion it is united with a portion of the scalenus ([Fig. 73], f‴).

Action.—Draws the sternum forward.

Mm. levatores costarum.—Small muscles having origin on the transverse processes of the thoracic vertebræ, passing caudoventrad, and becoming inserted on the angle of the rib lying immediately caudad of the origin. They are continuous with the external intercostals.

Relations.—Outer surface with the longissimus dorsi ([Fig. 69], f), and craniad with the iliocostal ([Fig. 69], h). Inner surface with the internal intercostals ([Fig. 69], k).

Action.—Pull the ribs dorsocraniad.

Mm. intercostales externi ([Fig. 73], m; [Fig. 69], i).—The external intercostals are placed in the outer portion of the intercostal spaces. They are composed of bundles of fibres attached by their ends to the adjacent borders of the ribs and having in general the direction of the external oblique muscle, i.e., they pass from their cranial ends caudoventrad. They occupy the intercostal spaces between the true ribs and extend even caudad into the spaces between the false ribs. They are lacking between the ventral ends of the costal cartilages of the first six to eight ribs, so that the internal intercostals ([Fig. 69], k) are here exposed. The more caudal external intercostals are more nearly craniocaudal in direction.

Relations.—Outer surface with obliquus abdominis externus ([Fig. 68], p), latissimus dorsi ([Fig. 68], m), serratus posterior inferior ([Fig. 73], n) and superior ([Fig. 73], l), serratus anterior ([Fig. 73], i), scalenus ([Fig. 73], f), and iliocostal ([Fig. 69], h). Inner surface with the internal intercostals ([Fig. 69], k).

Action.—Protractors of the ribs.

Mm. intercostales interni ([Fig. 69], k).—The internal intercostals are similar to the external intercostals, beneath which they lie. Their fibres pass between the ribs at nearly right angles to those of the external intercostals and have nearly the direction of the fibres of the internal oblique. They occupy all the intercostal spaces from the first to the thirteenth ribs.

Relations.—Outer surface with the external intercostals ([Fig. 69], i), and ventrad with the scalenus ([Fig. 73], f), transversus costarum ([Fig. 73], j), and rectus abdominis ([Fig. 73], k). Inner surface with the pleura and the transversus thoracis.

Action.—Retractors of the ribs.

M. transversus thoracis (triangularis sterni; sternocostalis internus).—This represents a thoracic portion of the transversus abdominis. It consists of five or six flat muscular bands lying on the inner surface of the thoracic wall.

Origin on the lateral borders of the dorsal face of the sternum, opposite the attachments of the cartilages of the third to the eighth ribs. The six bands thus formed, each about one centimeter wide, pass laterad and are inserted into the cartilages of the ribs near their junction with the ribs, and into the fascia which covers the inner surface of the internal intercostals in this region.

Relations.—Outer surface with the internal intercostals and the cartilages of the ribs. Inner surface with the pleura.

Diaphragma ([Fig. 74]).—The diaphragm consists of a central so-called semilunar tendon (e) and of muscular fibres which pass radially from the body wall to the tendon. It forms a complete oblique partition between the abdominal and thoracic cavities. The dorsal end is farther caudad than the ventral.

The central tendon (e) is thin and irregularly crescent-shaped, with the convexity ventrad and the horns of the crescent prolonged as two tendinous bands (e′) which end in two triangular membranous portions (d) of the diaphragm, one on each side of the spinal column. It is pierced by an opening for the vena cava (f).

[Fig. 74].—Diaphragm, Caudal Surface seen Obliquely from the Right.

a, right crus; b, left crus; c, c′, sternocostal part of diaphragm; d, d′, membranous portions of the diaphragm; e, central tendon; e′, prolongations of central tendon; f, opening for posterior vena cava; g, œsophagus; h, aorta; i, M. transversus abdominis.

The muscular portion is in two parts: (a) The vertebral portion (a, b) arises by a single tendon from the ventral surface of the second, third, and fourth lumbar centra. The tendon diverges into two, the right one (a) of which is much stronger, and from each of the two arise muscle-fibres. Each mass of fibres is one of the two crura (sing. crus) of the diaphragm. The aorta (h) enters the abdomen between the crura dorsally. The fibres of each crus diverge to be inserted into the central tendon and the dorsal continuation of its horn. The two sets of fibres unite ventrad of the opening of the aorta. Between this opening and the central tendon is another opening for the œsophagus (g); this lies entirely in that part of the diaphragm which arises from the right crus (a). The fibres are again united ventrad of the œsophageal opening.

(b) The sternocostal part (c, c′) takes origin from the xiphoid process and the last five ribs, by fleshy bundles which interdigitate with those of the transversus abdominis (i). The fibres converge to the central tendon (e). Between the crus of each side and the most dorsal of the costal fibres is the membranous interval (d) mentioned above.

4. Abdominal Muscles.

M. obliquus abdominis externus ([Fig. 68], p).—A large, thin sheet of muscle covering the whole abdomen and part of the thorax ventrally.

Origin.—(a) From the last nine or ten ribs by means of as many tendons, which are interconnected to form arches that span the slips of the serratus anterior. The muscle-fibres arise from these tendons and from their intervening arches. (b) From the lumbodorsal aponeurosis common to it and the internal oblique. The cranial fibres pass nearly ventrad, the caudal fibres caudad, and the intervening fibres take an intermediate course. The fibres end in a thin aponeurosis of insertion along a curved line which passes at first caudad and then laterodorsad. The aponeurosis fibres continue in the direction of the muscle-fibres to the

Insertion into the median raphe ventrad of the sternum from the insertion of the seventh costal cartilage to the xiphoid process, into the linea alba from the sternum to the pubic tubercle, and into the tubercle and the cranial border of the pubis. Caudad of the xiphoid process the aponeurosis is closely united to the superficial layer of the internal oblique, where it forms the outer layer of the sheath of the rectus abdominis. Laterad of the pubic tubercle the tendon is perforated by the inguinal canal. In the cat neither the caudal part of the muscle nor its tendon is attached to the ilium, as it is in man and the dog, so that no Poupart’s ligament, or inguinal ligament, is formed.

Relations.—Outer surface with the cutaneus maximus, the integument, and near the origin with the latissimus dorsi ([Fig. 68], m). Inner surface with the obliquus internus ([Fig. 73], o), the rectus abdominis ([Fig. 73], k), the intercostales externi ([Fig. 73], m), a small part of the serratus posterior inferior ([Fig. 73], n), and by its dorsal tendon with the longissimus dorsi ([Fig. 69], f).

Action.—Constrictor of the abdomen.

M. obliquus abdominis internus ([Fig. 73], o).—A thin sheet similar to the preceding but of less extent. Its fibres cross those of the external oblique nearly at right angles and lie beneath them.

Origin.—(1) Between the fourth and seventh lumbar vertebræ from the lumbar aponeurosis which is common to it and the external oblique. The lumbar aponeurosis takes origin from the lumbar spinous processes and the interspinous ligaments, and is continuous craniad with the aponeurosis of the serratus posterior inferior. Laterad it splits into three sheets, two for the above-named muscles and a third which passes to the vertebral transverse processes and forms the fascia covering the supraspinous muscles of the lumbar region. (2) By a similar aponeurosis from the ventral half of the iliac crest. (3) By fleshy fibres from the three crural arches. These are three delicate ligamentous arches which stretch from the crest of the ilium to the pubic spine. The dorsal one gives exit to the iliopsoas muscle, the middle to the femoral vessels, and the ventral to the spermatic cord. In the female the middle and ventral arches may fuse. The pillar between the dorsal and middle arches is attached to the iliopectineal eminence.

Insertion.—The fibres pass cranioventrad and end along a longitudinal line in a thin aponeurosis of insertion, which is united in the linea alba to those of the external oblique and transversus. At the caudal end of the aponeurosis all its fibres pass outside of the rectus abdominis ([Fig. 73], k). At its cranial end the fibres divide into two sheets or laminæ, one of which passes outside of the rectus and the other inside. The outer lamina unites with the aponeurosis of the external oblique, while the inner lamina unites with that of the transversus. There is thus formed a sheath for the cranial part of the rectus muscle.

Relations.—Outer surface with the obliquus externus ([Fig. 68], p). Inner surface with the transversus abdominis ([Fig. 69], l), and by its ventral tendon with the rectus.

Action.—Compressor of the abdomen.

M. transversus abdominis ([Fig. 69], l).—A thin sheet covering the whole surface of the abdomen and lying beneath the internal oblique. Its fibres are nearly transverse.

Origin.—(1) By fleshy fibres or by a thin aponeurosis from the cartilages of all the false and floating ribs, by interdigitation with the fibres of the diaphragm. (2) From the tips of all the lumbar transverse processes. (3) From the ventral border of the ilium. (4) From the dorsal and middle of the three crural arches, where it may blend partly with the internal oblique. The muscle is continuous craniad with the transversus thoracis muscle. Near the lateral border of the rectus abdominis the muscle ends in a thin aponeurosis of insertion which is continued (its fibres having the direction of the muscle-fibres) to the

Insertion in the linea alba.

Relations.—Outer surface with the internal oblique ([Fig. 73], o) and the rectus abdominis ([Fig. 73], k), dorsad also with the longissimus dorsi ([Fig. 69], f). Inner surface with a thin fascia covering the peritoneum and ventrocaudad with the rectus ([Fig. 73], k). The dorsal edge of the muscle touches the iliopsoas and longissimus dorsi; the ventral edge touches the muscle of the opposite side.

Action.—Constrictor of the abdomen.

M. rectus abdominis ([Fig. 73], k).—A rather thick, flat muscle which lies near the median ventral line separated by the linea alba from its fellow of the opposite side and stretching from the pubis to the first costal cartilage. Opposite the first lumbar vertebra it is approximately four centimeters wide. It narrows at both ends.

Origin by a strong tendon from the tubercle of the pubis. The muscle passes craniad at first between the peritoneal fascia and the transversus aponeurosis, then in the sheath formed by the internal and external oblique and the transversus aponeurosis. It emerges from the sheath opposite the xiphoid process and passes ventrad of the costal cartilages. Between the third and fourth costal cartilages it ends in a thin tendon which passes beneath the transversus costarum and is

Inserted into the first costal cartilage near its middle, into the second costal cartilage near its sternal end, and into the sternum between the first and fourth cartilages.

Relations.—Outer surface of the cranial part of the muscle and its tendon with the pectoralis minor ([Fig. 68], o) and the transversus costarum ([Fig. 73], j); caudad the muscle is covered by the outer layer of the rectus sheath. Lateral edge with the obliquus externus ([Fig. 68], p), obliquus internus ([Fig. 73], o), and transversus abdominis ([Fig. 69], l). Medial edge with the muscle of the opposite side. Inner surface with the internal intercostals ([Fig. 69], k) and the rib cartilages; the inner layer of the rectus sheath and the peritoneum.

Action.—Retracts the ribs and sternum and compresses the abdomen.