Chapter I: Muscles of the Shoulder Girdle

The =trapezius= is much thicker and broader than in the horse, and is undivided. It arises on the ligamentum nuchæ and supraspinous ligament, from the atlas to the twelfth thoracic vertebra.

The =omo-transversarius= is a muscle (not present in the horse) which arises on the wing of the atlas, and, inconstantly, the transverse process of the second cervical vertebra, and is inserted into the scapular spine and fascia.

The =rhomboideus= is clearly divided into cervical and dorsal portions, the latter extending further than in the horse.

The =latissimus dorsi= has a broad tendon of origin, which blends with the lumbo-dorsal fascia; it is also attached to the eleventh and twelfth ribs, the fascia over the external intercostal and oblique abdominal muscles, and by a tendinous slip to the deep pectoral muscle.

The =mastoido-humeralis= has two distinct parts. The dorsal division (M. cleido-occipitalis) arises on the occipital bone and the ligamentum nuchæ. The ventral part (M. cleido-mastoideus) is smaller and arises by a round tendon on the mastoid process and the rectus capitis anterior major, and by a thin tendon on the mandible. At the shoulder a small muscle which arises on the first rib blends with the deep face of the mastoido-humeralis.[75]

The =superficial pectoral= muscle does not present any striking difference.

The =deep pectoral= arises as far forward as the second rib and is undivided. However, the scapular portion may be considered to be represented by a small branch extending over the lower part of the supraspinatus. A tendon is detached from the dorsal edge, which blends with the latissimus dorsi and coraco-brachialis.

The =serratus magnus= is clearly divided into cervical and thoracic portions. The former is large and extends from the third (or second) cervical vertebra to the fifth rib, being overlapped behind by the thoracic part. The thoracic part is relatively thin and is covered by a very strong aponeurosis; it is attached to the fourth to the ninth ribs by six digitations, and is inserted by a flat tendon into the inner face of the dorsal angle of the scapula.

II. MUSCLES OF THE SHOULDER

The =deltoid= is clearly divided into acromial and scapular portions. The former arises on the acromion, the latter on the posterior border of the scapula and the aponeurotic covering of the infraspinatus. The scapular part of the muscle is largely inserted into the fascia covering the triceps.

The =supraspinatus=, =infraspinatus=, and =teres minor= do not differ materially from those of the horse.

The =subscapularis= consists of three portions with a common tendon of insertion.

The =teres major= and =coraco-brachialis= resemble those of the horse.