Myology
M. pectoralis thoracica, Fig. 5. The origin is from approximately the ventral third of the keel, the lateral and anterior portion of the clavicle and the adjacent sterno-coraco-clavicular membrane, and from the lateral portion of the sternum and the fascia overlying the thoracic ribs. This massive muscle covers the entire ventral surface of the thorax, converges, and inserts on the pectoral surface on the ventral side of the humerus.
M. supracoracoideus, Fig. 5. The origin is from the dorsal two-thirds of the keel and medial half of the sternum (where the origin is bordered ventrally, posteriorly, and laterally by the origin of M. pectoralis thoracica) and from the sterno-coraco-clavicular membrane adjacent to the coracoid. This large pinnate muscle converges, passes through the foramen triosseum, and inserts by means of a strong tendon on the dorsal surface of the humerus on the deltoid ridge.
M. coracobrachialis posterior, Fig. 5. The origin is from a prominent lateral wing on the posterolateral portion of the coracoid, and from the lateral surface of the proximal two-thirds of the coracoid. The insertion is by means of a tendon on the internal tuberosity of the humerus. Of the muscles described here, this one differs most strikingly from the homologous muscle in P. subis. The difference can be seen by comparing Figs. 1 and 5.
M. sternocoracoideus, Figs. 5, 6, and 7. The origin is from the external, and to a slight extent from the internal, surface of the costal process. The insertion is on a posterolateral triangular area on the dorsal surface of the coracoid.
M. costi-sternalis, Figs. 5 and 6. The origin is from the anterior edge of the sternal portion of the first three thoracic ribs. The muscle converges and inserts on the apex of the costal process.
M. subcoracoideus (ventral head), Fig. 6. The origin is from the manubrium and from approximately the posterior half of the coracoid and on the medial and dorsal surface of that bone, and the medial side of the sterno-coraco-clavicular membrane adjacent to the coracoid. The ventral head passes anterodorsally to join with the dorsal head (not here described), and the combined muscle inserts by a tendon on the internal tuberosity of the humerus.
Mm. intercostales externus, Fig. 5. These muscles extend posteroventrally between successive thoracic ribs and between the last cervical and first thoracic ribs.
Mm. intercostales internus, Fig. 7. These muscles extend anteroventrally between the last three thoracic ribs.
Costopulmonary muscles, Fig. 7. This series of muscle slips from the thoracic ribs attaches to the aponeurosis covering the lungs.