364 NEUROLOGY, OR ANATOMY OF NERVOUS SYSTEM 







cutaneous of the ulna, and they all terminate at the base of the 

 second phalanx. 



The posterior interosseous passes between the planes of the 

 supinator brevis, around the outer side of the neck of the 

 radius, and runs beneath the superficial muscles on the back 

 of the forearm and on the lower part of the interosseous mem- 

 brane. It supplies all the muscles of the back and outer part 

 of the forearm except the supinator longus, extensor carpi 

 radialis longior, and the anconeus, and terminates at the 

 wrist in a ganglion from which are supplied the carpal liga- 

 ments and joint. 



The Dorsal Nerves 



The posterior divisions in the dorsal region: The external 

 branches increase in size from above downward, pierce the 

 longissimus dorsi to supply the erector spinse group, and those 

 of the lower six, the skin. The internal branches of the six 

 upper supply the multifidus and semispinalis dorsi and the 

 skin. The six lower internal supply the multifidus, but not 

 the skin. 



The Anterior Divisions of the Dorsal Nerves 



First Dorsal. The anterior division in part joins the brachial 

 plexus, and the remainder of the nerve forms the first inter- 

 costal, which has no lateral cutaneous branch. 



The UPPER six are called the pectoral intercostal nerves, 

 and lie below the vessels. At first they run between the pleura 

 and the external intercostal muscles, then between the two 

 planes of muscles to the middle of the rib, here giving off the 

 lateral cutaneous nerves. The nerves now enter the substance 

 of the internal intercostals as far as the cartilages, where they 

 lie between the muscles and the pleura. Finally they cross 

 the internal mammary vessels and the triangularis sterni, 

 pierce the internal intercostals and pectoralis major, and end 

 in the skin of the chest, as the anterior cutaneous nerves of the 

 thorax. 



Branches. Muscular, to the intercostals, triangularis, 

 levatores costarum, and serratus posticus superior. 



The lateral cutaneous are given off about midway to the 



