also cut the serratus magnus, and rhomboideus close to their attach- 

 ments to the scapula thus leaving the arm attached to the body only by 

 the nerves of the brachial plexus. Before attempting to expose farther the 

 ventral divisions of the 6th, if present, 7th and 8th cervical and the 

 1st and 2d thoracic nerves, first note on a skeleton the relation of the first 

 two ribs to the 6th, 7th and 8th cervical and the ist and 2d thoracic inter- 

 vertebral foramina, through which the above mentioned nerves emerge from 

 the spinal cord. Now place the arm in such a position that the whole of 

 the thoracic portion of the M. serratus magnus is exposed. Carefully 

 remove the small portion of the M. scalenus that lies dorsal to the brachial 

 plexus taking care not to cut any of the nerves. The large nerve to the 

 thoracic portion of the serratus magnus arises from the 7th and 8th cervi- 

 cals (or from the 8th only) and extends posteriorly on the surface of the 

 serratus magnus to which it is distributed. This nerve, more or less covered 

 by connective tissue, may emerge from between the dorsal and ventral 

 portions of the scalenus, or it may pass through the small dorsal portion of 

 the muscle. After tracing the nerve, cut it 15 to 20 cm. from its origin. 

 The ventral divisions of the 7th and 8th cervical nerves are readily exposed ; 

 the 1st and 2d thoracic nerves however, are covered by the ribs of which 

 the first one must be cut in order to expose the nerves. Remove enough 

 of the serratus magnus to expose the first rib. Cut the rib a little ventral 

 to the A. Axillaris, also cut it close to the tuberosity of the rib and remove 

 the detached portion. The A. cervicalis inferior should now be traced to 

 its place of origin from the A. Axillaris. With a little care the ventral 

 divisions of the first two thoracic nerves may be found and cut close to 

 the intervertebral foramina; the 7th and 8th cervical nerves also should 

 be cut close to the vertebrae and the arm removed. 



Nn. pectorales. Before attempting to demonstrate the nerves to the 

 pectoral muscles first carefully remove the connective tissue and fat from 

 the nerves of the brachial plexus using for this purpose the forceps, the back 

 of the scalpel, or some other non cutting instrument. The origin of the 

 pectoral nerves vary somewhat in different individuals. The following 

 disposition however, is common. The most cephalic or anterior of the 

 pectoral nerves originates from the 7th and 8th cervicals and is distributed 

 wholly to the anterior deep pectoral muscle (PI. I, 27). The nerve enters 

 the muscle a little dorsal to the cephalic vein where it crosses the anterior 

 deep pectoral. A communicating branch between this nerve and the 

 phrenic is quite commonly present. The nerves to the superficial pectoral 

 muscles arise from the loop or arch formed by the N. musculo-cutaneous 

 (PI. I, 29) and the N, medianus (PI. I, 32) immediately beneath the A. axil- 



