THE CAT 239 



but the main nerves forming it can be easily identified. The fol- 

 lowing are the principal nerves which leave the plexus : 



The radial nerve is the largest. It arises from the seventh and 

 eighth cervical and first thoracic nerves, and is distributed to the 

 muscles and skin of the foreleg. 



The median nerve, which is formed by the union of branches 

 from the seventh and eighth cervical and first thoracic nerves, 

 and the ulnar nerve, which springs from the eighth cervical and 

 the first thoracic, are large nerves which accompany the brachial 

 artery into the leg. 



The musculocutaneous nerve is formed by the union of branches 

 of the sixth and seventh cervical nerves. It supplies the biceps 

 and other muscles of the upper arm and the skin of the forearm. 



The axillary nerve is formed by branches of the sixth and 

 seventh cervical nerves and passes to the muscles and skin of 

 the shoulder. 



The subscapular nerves are three in number ; they arise from 

 the sixth, seventh, and eighth cervical nerves and go to the sub- 

 scapular muscle, on the inner surface of the scapula. 



The suprascapular nerve arises from the sixth cervical nerve and 

 goes to the muscles of the outer surface of the scapula and to the 

 integument of the upper arm. 



The phrenic nerve is formed by the union of a branch from the 

 fifth and one from the sixth cervical nerve ; it passes directly back, 

 at first along the subclavian artery, to the diaphragm. 



Exercise 31. Draw a diagram of the brachial plexus and the nerves 

 which issue from it, so far as observed. 



The thoracic spinal nerves, with the exception of the first, do 

 not enter a plexus but go directly to the muscles of the back and 

 side. Their dorsal rami are small ; their ventral rami are large 

 and are called the intercostal nerves ; each lies alongside the hinder 

 border of a rib, together with the intercostal artery. Find one of 

 these nerves and trace it to the backbone, where the dorsal ramus 

 will also be seen. 



The first three lumbar spinal nerves do not enter a plexus. 

 Their ventral rami divide, a short distance from their medial ends, 



