308 



THE SPINAL NERVES. 



generally very small, and it sometimes joined only one. in other cases both, of the divisions of 

 the first nerve (Journ. Anat., xi, 539). 



UPPER OR PECTORAL INTERCOSTAL NERVES. 



In their course to the fore part of the chest, these nerves accompany the inter- 

 costal blood-vessels. From the intervertebral foramina they are directed outwards in 

 front of the superior costo-transverse ligaments, the levatores costarum and the 

 external intercostal muscles, being covered anteriorly, as far as the angles of the ribs, 

 only by the pleura and the thin layer of connective tissue known as the endothoracic 

 fascia. Gaining the upper part of the corresponding intercostal spaces, where they 

 are placed below the intercostal vessels, the nerves next run between the external and 

 internal intercostal muscles, and soon give off the large lateral cutaneous branches, 



Fig. 202. PLAN OP AN UPPER DORSAL NERVE. 

 (G. D. T.) 



which accompany the prolongations of 

 the trunks for a short distance, and 

 then bend outwards through the ex- 

 ternal intercostal muscles about mid- 

 way between the spine and the sternum. 

 The nerves themselves, much reduced 

 in size, are now continued forwards 

 amid the fibres of the internal 

 intercostal muscles as far as the costal 

 cartilages, where they again come into 

 close relation with the pleura. In 

 approaching the sternum they cross in 

 front of the internal mammary vessels 

 and the triangularis sterni ; and finally 

 they pierce the internal intercostal 

 muscles and the greater pectoral, to 

 end in the integument of the breast, 

 receiving the name of the anterior 

 cutaneous nerves of the thorax. 



BRANCHES. Muscular branches are furnished by the intercostal nerves in the 

 first part of their course to the levatores costarum, and, from the upper four nerves, 

 to the serratus posticus superior. Several twigs enter the intercostal muscles with 

 which the nerves are in relation. At the fore part of the chest the triaogularis 

 sterni is supplied by offsets of these nerves from the second or third to the sixth ; 

 and from the fifth and sixth nerves branches pass to the upper end of the rectus 

 abdominis. 



Minute subcostal branches perforate the internal intercostal muscles to reach 

 the inner surface of the ribs, where they are distributed to the. periosteum and bone, 

 as well as probably to the costal pleura (Testut) ; and, according to Luschka, fine 

 sternal twigs are given off at the anterior ends of the intercostal spaces to the 

 back of the sternum. 



The lateral cutaneous nerves of the thorax pierce the external intercostal 

 and serratus magnus muscles, in a line a little behind the pectoral border of the 

 axilla. The first intercostal usually gives no lateral branch, or only a slender twig 

 to the axilla, but when that of the second nerve is unusually small, it may be supple- 

 mented by a branch of the first. The branch from the second intercostal is named 

 mtercosto-humeral, and requires separate description. Each of the remaining latera 



