1044 



THE NERVE SYSTEM 



giving off muscular branches, and terminates on the anterior part of the thorax 

 by forming the first anterior cutaneous nerve (ramus cutaneus anterior n. inter- 

 costalis /) of the thorax. Occasionally this anterior cutaneous branch is wanting. 

 The first intercostal nerve, as a rule, gives off no lateral cutaneous branch, but 

 sometimes a small branch is given off which communicates with the intercosto- 

 humeral. It frequently receives a connecting twig from the second thoracic 

 nerve, which passes upward over the neck of the second rib. 



Anterior aspect. 



Posterior aspect. 



FIG. 766. Distribution of cutaneous nerves. 



The Anterior Divisions of the Second, Third, Fourth, Fifth, and Sixth Thoracic Nerves 

 and the Small Branch from the First Thoracic Nerve (nn. intercostales] are confined 

 to the parietes of the thorax, and are named thoracic intercostal nerves. They 

 pass forward in the intercostal spaces below the intercostal vessels. At the back 

 of the thorax they lie between the pleura and the posterior intercostal membrane, 

 piercing the latter, and course between the two planes of Intercostal muscles as 

 ifar as the middle of the rib. They then enter the substance of the Internal 

 intercostal muscles, and, running amidst their fibres as far as the costal cartilages, 

 they gain the inner surface of the muscles, and lie between them and the pleura. 



