Anatomy of the Cat

by Jacob Reighard; H. S. Jennings

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).