BRACHIAL PLEXUS. 235 



It supplies the glands, and ends in the wall of the thorax below the pre- 

 ceding. 



The subscapular branch (fig. 70, c) courses with a nerve of the same 

 name along the subscapularis, as far as the lower angle of the scapula, 

 where it ends in branches for the serratus magnus, and the latissimus dorsi 

 and teres muscles: it gives many offsets to the glands of the space. 



Near its origin the artery sends backwards a considerable dorsal branch 

 round the edge of the subscapular muscle : this gives an infrascapular 

 offset to the ventral aspect of the scapula, and then turns to the dorsum of 

 that bone, where it will be afterwards dissected. 



The subscapular artery is frequently combined at its origin with other 

 branches of the axillary, or with branches of the brachial artery. 



The circumflex bi-anches (anterior and posterior) arise near the border 

 of the subscapular muscle. One turns in front of, and the other behind 

 the humerus. They will be followed in the examination of the arm. 



Small muscular offsets enter the coraco-brachialis muscle. 



The AXILLARY VEIX (ff) continues upwards the basilic vein of the arm 

 and has the same extent and connections as the axillary artery. It lies to 

 the thoracic side of its artery, and receives thoracic and shoulder branches. 

 Opposite the subscapular muscle it is joined externally by a large vein, 

 which is formed by the union of the venae comites of the brachial artery ; 

 and near the clavicle the cephalic vein opens into it. 



Dissection. To follow out the branches of the brachial plexus, cut 

 through the pectoralis minor near its insertion into the coracoid process, 

 and turn it towards the chest, but without injuring the thoracic nerves in 

 contact with it. The axillary vessels are next to be cut across below the 

 second rib, 1 and to be drawn down with hooks ; and their thoracic branches 

 may be removed at the same time. A dense fascia is to be cleared away 

 from the large nerves of the plexus. 



The BRACHIAL PLEXUS results from the union of the anterior branches 

 of the four lower cervical nerves with the first dorsal (in part) ; and a slip 

 is added to it above from the lowest nerve in the cervical plexus. It is 

 placed partly in the neck, and partly in the axilla, and is divided opposite 

 the coracoid process into large trunks for the supply of the limb. The 

 part of the plexus above the clavicle is described in the dissection of the 

 head and neck (p. 79). The part below the clavicle has the same connec- 

 tions with the surrounding muscles as the axillary artery. The nerve 

 trunks interlace in it generally in the following manner : 



At first the plexus consists of two bundles of nerves, which lie on the 

 outer side of the artery, and are thus constituted ; the one nearest the 

 vessel is formed by the last cervical with the part of the first dorsal nerve ; 

 and the other, by the fifth, sixth, and seventh cervical nerves. A little 

 lower down a third or posterior cord is produced by the union of two fas- 

 ciculi, one from each of the other bundles ; so that, beneath the small pec- 

 toral muscle, the plexus consists of three large cords, one being on the 

 outer side, another on the inner side, and the third behind the vessel. 

 Occasionally there may be some deviation from the above mentioned 

 arrangement. 



The branches of the plexus below the clavicles arise from the several 

 cords in the following way : 



1 The student must be careful not to cut the vessels higher than tlie spot men- 

 tioned, otherwise he will injure the dissection of the neck. 



