ANTERIOR THORACIC NERVES 



1045 



Near the sternum, they cross- in front of the internal mammary artery and Tri- 

 angularis sterni muscle, pierce the Internal intercostal muscles, the anterior 

 intercostal membrane, and Pectoralis major muscle, and supply the integument 

 of the anterior wall of the thorax and over the mammary gland, forming the 

 anterior cutaneous nerves of the thorax; the branch from the second nerve is 

 joined with the supraclavicular nerves of the cervical plexus. 



Branches. Numerous slender muscular filaments (rami musculares] supply the 

 Intercostals, the Infracostales, the Levatores costarum, the Serratus posticus 

 superior, and the Triangularis sterni muscles. At the front of the thorax some 

 of these branches cross the costal cartilages from one intercostal space to another. 



/INTERNAL BRANCH 

 (CUTANEOUS) 



EXTERNAL BRANCH, 

 (MUSCULAR) 



ANTERIOR CUTANEOUS 



FIG. 767. Plan of a typical intercostal nerve. (W. Keiller.) . < 



The lateral cutaneous nerves (rami cutanei laterales] are derived from the inter- 

 costal nerves, midway between the vertebras and sternum; they pierce the External 

 intercostal and Serratus magnus muscles, and divide into anterior and posterior 

 brandies. The anterior branches (rami anteriores] are reflected forward to the 

 side and fore part of the thorax, supplying the skin of the thorax and mamma; 

 those of the fifth and sixth nerves supply the upper digitations of the External 

 oblique. The posterior branches (rami posteriores) are reflected posteriorly 

 to supply the integument over the scapula and over the Latissimus dorsi muscle. 



The lateral cutaneous branch of the second intercostal nerve (n. inter costobrachi alt x) 

 is of large size, and does not divide, like the other nerves, into an anterior and a 

 posterior branch. It is named, from its origin and distribution, the intercosto- 

 humeral or intercostobrachial nerve (Figs. 751 and 764). It pierces the External 

 intercostal muscle, crosses the axilla to the inner side of the arm, and joins with 

 a filament from the lesser internal cutaneous nerve of the upper arm (nerve of 

 Wrisberg). It then pierces the fascia, and supplies the skin of the upper half of 



