414 



BRACHIAL PLEXUS. 



Fig. 1S6. 



pital artery. The occipitalis majoi 

 sends numerous branches to the mus- 

 cles of the neck, and is distributed 

 to the integument of the scalp, as far 

 forwards as the middle of the vertex 

 of the head. Its branches commu- 

 nicate with those of the occipitalis 

 minor. 



BRACHIAL PLEXUS. 



The Brachial or axillary plexus of 

 nerves is formed by communications 

 between the anterior branches of the 

 four last cervical and first dorsal 

 nerve. These nerves are all similar 

 in size, and their mode of disposition 

 in the formation of the plexus is the 

 following : the fifth and sixth nerves 

 unite to form a common trunk, which 

 soon divides into two branches ; the 

 last cervical and first dorsal also 

 unite immediately upon their exit 

 from the intervertebral foramina, and 

 the common trunk resulting from their 

 union after a short course also di- 

 rides into two branches ; the seventh 

 nerve passes outwards between the 

 common trunks of the two preceding, ?nd opposite the clavicle divides 

 into a superior branch which unites with the inferior division of the supe- 

 rior trunk, and an inferior branch which communicates with the superior 

 division of the inferior trunk : from these divisions and communications 

 the brachial plexus results. The brachial plexus communicates with the 

 cervical plexus by means of a branch sent down from the fourth to the 

 fifth nerve, and by the inferior branch of origin of the phrenic nerve, and 

 also sends filaments of communication to the sympathetic. The plexus is 

 broad in the neck, narrows as it descends into the axilla, and again en- 

 larges at its lower part where it divides into its six terminal branches. 



Relations. The brachial plexus is in relation in the neck with the two 

 scaleni muscles, between which its nerves issue ; lower down it is placed 

 between the clavicle and subclavius muscle above, and the first rib and 

 first serration of the serratus magnus muscle below. In the axilla, it is 

 situated at first to the outer side and then behind the axillary artery, rest- 

 ing by its outer border against the tendon of the subscapularis muscle. At 

 this point it completely surrounds the artery by means of the two cordi 

 which are sent off to form the median nerve. 



Its Branches may be arranged into two groups, humeral and descend- 

 ing, 



A view of the brachial plexus of nerves and branches of arm. 1, 1. The scalenug 

 milieus muscle, in front of which are the roots of the plexus. 2, 2. The median nerve 

 3. The ulnar nerve. 4. The branch to the biceps muscle. 5. The nerves of Wrisberg 

 6, The phrenic nerve from the 3d and 4th cervical. 



