236 DISSECTION OF THE UPPER LIMB. 



The outer cord gives origin to one anterior thoracic branch, the musculo- 

 cutaneous trunk, and the outer head of the median nerve. 



The inner cord produces a second anterior . thoracic nerve, the inner 

 head of the median, the internal cutaneous, the nerve of Wrisberg, and 

 the ulnar nerve. 



The posterior cord furnishes the subscapular branches, and ends in the 

 circumflex and musculo-spiral trunks. 



Only the thoracic and subscapular nerves are dissected to their termina- 

 tion at present ; the remaining nerves will be seen in the arm. 



The anterior thoracic branches (fig. 70, l and 2 ), two in number, are 

 named outer and inner, like the cords from which they come. 



The outer nerve crosses inwards over the axillary artery, to the under 

 surface of the great pectoral muscle in which it ends. On the inner side 

 of the vessel it communicates with the following branch. 



The inner thoracic branch turns upwards between the arteiy and vein, 

 and after receiving the offsets from the other, ends in many branches to 

 the under surface of the pectoralis minor. Some twigs enter the great 

 pectoral muscle, after passing either through the pectoralis minor or above 

 its border. 



The subscapular nerves are three in number, and take their names from 

 the muscles supplied : 



The branch of the subscapularis is the highest and smallest, and enters 

 the upper part of that muscle. 



The nerve of the teres major gives a small offset to the inferior part of 

 the subscapularis, and ends in its muscle. 



A long nerve of the latissimus dorsi ( s ) takes the course of the sub- 

 scapular artery along the posterior wall of the axilla, and enters the fleshy 

 fibres near the outer end. 



Another small nerve, nerve to the serratus ( 4 ) (posterior thoracic), lies 

 on the surface of the serratus muscle. It arises above the clavicle (p. 

 80), from the fifth and sixth cervical nerves ; it descends behind the axil- 

 lary artery, and enters that surface of the serratus magnus which is turned 

 towards the axilla. 



The LATISSIMUS DORSI MUSCLE, G, may be examined as far as it enters 

 into the posterior fold of the axilla. Arising from the spinal column and 

 the back of the trunk, and crossing the lower angle of the scapula, the 

 muscle ascends to be inserted into the bottom of the bicipital groove by a 

 tendon, one inch and a half in width, in front of the teres ; at the lower 

 border aponeurotic fibres connect the two, but a bursa intervenes between 

 them near the insertion. 



Dissection. To lay bare the serratus muscle between the side of the 

 chest and the base of the scapula, the arm is to be drawn from the trunk, 

 so as to separate the scapula from the thorax. The nerves of the brachial 

 plexus may be cut through opposite the third rib ; and the fat and fascia 

 should be cleaned from the muscular fibres. 



The SERRATUS MAGNUS MUSCLE (fig. 71, A) extends between the 

 scapula and the thorax. It arises by nine pointed processes from the outer 

 surface of the eight upper ribs, the second rib having two pieces ; and 

 between the ribs it takes origin from the aponeurosis covering the inter- 

 costal muscles. The fibres converge towards the base and angles of the 

 scapula, but from a difference in their direction the muscle appears to 

 consist of three parts. 



The upper part is attached internally to the first two ribs and an 



