6 THE UPPER EXTREMITY 



Dissection. In searching for a cutaneous nerve, cut boldly down through 

 the superficial fascia in the direction in which the nerve runs until the 

 plane at which the superficial and deep fascia blend is reached. It is here 

 that the main trunks are to be found ; and in a well-injected subject the 

 cutaneous arteries furnish the best guides. 



Nervi Cutanei, Arteriae Cutaneae (Cutaneous Nerves and 

 Arteries). There are three distinct groups of cutaneous 

 nerves for the supply of the skin on the anterior and lateral 

 parts of the thorax. They are : 



1. The supraclavicular nerves from the cervical plexus. 



2. The anterior cutaneous, \from the anterior rami (intercostal) 



3. The lateral cutaneous, J of the thoracic nerves. 



The supraclavicular nerves arise in the neck from 

 the third and fourth cervical nerves, and, spreading out as 

 they descend, they cross the clavicle under cover of the 

 platysma. They are classified, according to their positions, 

 into the anterior, the medial, and the posterior branches. 

 The anterior are the smallest of the series ; they cross the 

 medial part of the clavicle to end in the skin immediately 

 below. The medial branches pass over the middle of the 

 clavicle and extend downwards, in the superficial fascia 

 over the pectoralis major, as far as the third rib. The 

 posterior cross the lateral third of the clavicle, and will 

 be afterwards followed to the skin of the shoulder. 



These nerves can readily be found by cutting down upon the clavicle 

 through the platysma, and in the direction of its fibres. 



The anterior cutaneous nerves are the minute terminal twigs 

 of the anterior branches of the thoracic nerves. They 

 become superficial by piercing the pectoralis major muscle 

 and deep fascia close to the margin of the sternum. One 

 will be found in each intercostal interval, and they are 

 accompanied by the cutaneous perforating branches of the internal 

 mammary artery, which (when injected) serve as the best guides 

 to the nerves. They give slender twigs to the skin over 

 the sternum, and larger branches which are directed laterally, 

 and may be traced as far as the anterior fold of the axilla. 



The lateral cutaneous nerves^ much larger than the pre- 

 ceding, arise from the anterior rami of the thoracic nerves, 

 and appear on the side of the thorax, along a line situated 

 a little behind the anterior fold of the axilla. They pierce 

 the wall of the thorax in the interspaces between the 

 ribs, and divide into anterior and posterior branches under 



