126 S. R. DETWILER 
4. M. pectoralis. This constitutes a triangular-shaped muscle 
taking origin from the aponeurosis between it and the m. obliquus 
externus abdominis, the linea alba, and from a cartilaginous ster- 
num. Its fibers converge into a short tendon which inserts on 
the distal part of the processus lateralis humeri. 
Innervation: n. pectoralis, a branch of the common trunk 
formed by the union of the fourth and fifth spinal nerves (fig. 
2, pC.) 
5. M. subcoraco-scapularis. This is a short, thick muscle 
which takes origin from the medial side of the contiguous portions 
of the scapula and the procoracoid. The fibers pass out across 
the inner aspect of the shoulder joint and insert on the medial 
surface of the proximal part of the humerus. 
Innervation: n. subscapularis, a branch of the third spinal 
nerve (fig. 2, n. sb. sc.). 
6. M. latissimus dorsi. This is a broad triangular muscle 
which arises from an aponeurosis between it and the longitudinal 
dorsal trunk muscles. The fibers converge into a long tendon, a 
part of which unites with the tendon of origin of the m. anconaeus 
scapularis medialis; the remainder passes across the lateral as- 
pect of the shoulder capsule and inserts on the proximal dorso- 
lateral surface of the humerus close to the processus lateralis 
humeri. 
Innervation: n. latissimus dorsi, a branch of the fourth spinal 
nerve (fig. 2, n. lt. dor.). 
7. M. coraco-brachialis brevis. This is a short, rather thick 
muscle which takes origin from the posterior margin and from 
the outer surface of the posterior part of the coracoid, internal 
to the m. supracoracoideus. The muscle passes to the medio- 
ventral surface of the humerus and inserts on its proximal two- 
fifths and under cover of the fibers of the m. brachialis inferior 
(m. biceps brachii). 
Innervation: by the n. coraco-brachialis, a branch of the 
fourth and fifth spinal nerves (fig 2. 7. cor. br.). 
8. M. coraco-brachialis longus. This is a long, rather thick 
muscle which takes origin from the internal posterior margin of 
the coracoid close to the glenoid cavity. It passes out along the 
