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).