278 



THE CAT. 



[CHAP. ix. 



plexus, placed opposite the first four vertebrae below the sterno- 

 mastoid muscle, and connected, near the skull, with the pneumo- 

 gastric, hypoglossal, and sympathetic nerves. 



The fifth and sixth cervical nerves give off a branch called the 

 phrenic nerve, which passes backwards between the pleura and the 

 pericardium, and is distributed to the diaphragm. 



18. The three posterior cervical nerves unite to form an inter- 

 lacement called the BRACHIAL PLEXUS, which is of much greater size 



than the cervical plexus, and 

 gives origin to the nerves of the 

 FORE -LIMB. It is reinforced by 

 the first dorsal nerve, and the 

 plexus extends down from the 

 lower part of the neck to the 

 axillary space. 



The connexions formed by the 

 nerves in the plexus are some- 

 what apt to vary, but the fol- 

 lowing conditions appear to be 

 normal. A large branch from 

 the eighth cervical nerve unites 

 with the main branch of the 

 first dorsal to form a trunk 

 which (after giving off a small 

 branch to help to form the me- 

 dian) continues on as the ulnar 

 nerve (Fig. 131, v). Delicate 

 branches from the first dorsal 

 and eighth cervical also unite 

 to form the internal cutaneous 

 nerve (ic). The median nerve is 

 formed by the junction of the 

 small offshoot from the ulnar 

 (already mentioned), with a 

 branch from the seventh cer- 

 vical nerve. The largest branch 

 of the seventh, however, unites 

 with a considerable branch from the eighth cervical to form the 

 mttsculo-spiral nerve. From close to the root of the seventh cervical 

 the external respiratory nerve of Bell passes backwards. The musculo- 

 cutaneous nerve is formed by the junction of slender branches from 

 the sixth and seventh cervical nerves, and from the junction of two 

 stouter branches from the same two nerves there arise the circumflex 

 and the subscapular nerves. Another subscapular nerve is formed 

 by the junction of very slender branches from the sixth and seventh 

 cervical nerves, while from the sixth there springs a very consider- 

 able supra-scapular nerve, and a small branch which goes to the 

 rhomboideus muscle. 



The internal cutaneous nerve, as its name implies, passes to the 



1D 



Fig. 131. DIAGRAM OF THE RIGHT BRACHIAL 

 PLEXUS. 



(5(7, 7C, and 8C. Sixth, seventh, and eighth cer- 

 vical nerves. 

 1 D. First dorsal nerve. 

 /. Circumflex nerve. 

 tc. Internal cutaneous nerve. 

 . Median nerve. 

 me. Musculo-cutaneous nerve. 

 ms. Musculo-spiral nerve. 

 r. Nerve to rhomboideus muscle. 

 rb. Respiratory nerve of Bell. 

 sb. Subscapular nerves. 

 sps. Supra-scapular nerve. 

 v. Ulnar nerve. 



