the superficial stirface of the anterior deep pectoral and then runs in the 

 groove formed by this muscle and the mastoido-humeralis, as already seen, 

 and terminates in the mastoido-himieralis. Small branches are supplied 

 to the posterior cervical lymph glands, the cervical pannicidus, the stemo- 

 mandibularis, stemo-thyrohyoideus, anterior superficial pectoral and a 

 small branch to the region of the presternum. The dorsal branch extends 

 antero-dorsally along the anterior border of the anterior deep pectoral 

 muscle. It passes beneath the prescapular lymph gland and between the 

 muscles subscapulo-hyoideus and mastoido-humeralis to the latter of which 

 it is principally distributed. It also gives off branches to the anterior 

 deep pectoral muscle and to the posterior cervical and prescapular l3miph 

 glands. 



The ventral portion of the M. scalenus intervenes between the axillary 

 blood-vessels and the nerves that form the brachial plexus. The brachial 

 plexus is formed by the ventral divisions of the 6th, 7th and 8th, cervical 

 and the ist and 2d thoracic nerves, as will be demonstrated later. Cut 

 the dorsal branch of the A. cervicalis inferior and carefully remove the 

 connective tissue that stirrounds the large nerve trunks of the brachial 

 plexus. 



N. phrenicus or diaphragmatic nerve originates from the ventral divisions 

 of the 6th and 7th cervical nerves; occasionally it receives a small branch 

 from the 5th cervical also. The two or three radicals of the phrenic 

 nerve extend obliquely across the superficial face of the M. scalenus and at 

 its ventral border unite to form a single trunk, just as the nerve enters the 

 thorax, or a short distance within the thoracic cavity. Dissect up from the 

 siuface of the scalenus the two or three radicals of the N. phrenicus. Im- 

 mediately after crossing the A. cervicalis inferior the N. phrenicus receives 

 a small communicating branch from the inferior cervical ganglion of the 

 sympathetic nerve. The course of the phrenic nerve through the thoracic 

 cavity to the diaphragm will be studied when the thoracic portion of the 

 vagus and sympathetic nerves are traced. 



Exposure of the brachial plexus and removal of the thoracic limb. 



Expose as follows, the ventral divisions of the nerves that form the 

 brachial plexus, viz., the 6th (not constant), 7th and 8th cervical and the 

 1st and 2d thoracic. Cut the N. phrenicus at the first rib. Remove a 

 section of the ventral portion of the M. scalenus opposite the 6th, 7th, and 

 8th intervertebral foramina. Cut the skin and the Mm. panniculus 

 and latissimus, some distance (30 to 50 cm.) posterior to the scapula; cut 

 the skin and both portions of the trapezius close to the ligamentum nuchae; 



