386 NERVOUS SYSTEM. 
(4) and fifth are distributed to the muscles and integument of 
the sides of the neck. A branch of the fourth supplies the in- 
tegument in the hollow of the shoulder, and one fromm the fifth 
follows the vena cephalica and supplies the integument over 
the shoulder. The fifth by sending a branch to aid in forming 
the phrenic nerve (Fig. 157, 7) may be considered to enter 
partly into the brachial plexus. 
Owing to the intercommunicating branches between the 
ventral roots of the first five cervical nerves, these are some- 
times considered as forming a loose plexus which receives the 
name cervical plexus. 
The sixth, seventh, and eighth cervical nerves (with a part 
of the fifth) become interconnected with each other and with 
the first thoracic to form the brachial plexus. 
The Brachial Plexus (Fig. 159).—The brachial plexus is 
formed by the ventral rami of the fifth, sixth, seventh, and 
eighth cervical nerves and the first thoracic. Of the fifth cer- 
vical only a small part enters into the plexus, forming part of 
the phrenic nerve. The formation of the plexus is due to the 
union of the different nerves by means of strong connecting 
branches or ans@. The plexus lies in the axilla, along with 
the axillary artery and vein; all its component nerves pass 
laterad in front of the first rib. Its branches: supply the arm 
and shoulder. . 
The precise arrangement of the different strands is 
somewhat variable. The plexus is commonly made up in 
approximately the following manner (Fig. 159). From the 
fifth cervical nerve (V) a small branch joins a similar one 
from the sixth to form the phrenic nerve (a); the remainder of 
the fifth does not enter into the plexus. From the sixth cer- 
vical (VI) arise parts of the phrenic nerve (a), the suprascapular 
(8), the cranial one of the three subscapular nerves (c), the 
axillary (7), and the musculocutaneus (f). The sixth also 
gives off close to its origin a nerve (6’) which passes to the 
inner surface of the levator scapule and ramifies over the sur- 
face, supplying this muscle and extending to the rhomboideus, 
which it also innervates. The seventh cervical (VZ/) is the 
largest nerve entering into the plexus; it furnishes parts of one 
