UPPEE DOESAL NEEYES. 595 



posterior interosseous division distributes nerves to tne remaining 

 muscles on the outer and back part of the forearm, except the 

 anconeus (previously supplied), viz., to the short supinator and the 

 extensors. 



Cutaneous nerves are distributed, from the trunk of the nerve and 

 its radial division, to the lower part of the upper arm, to the forearm, 

 and to the hand — on the posterior and outer aspect of each. 



Varieties. — The dorsal branch of the radial nei-ve sometimes supplies the 

 whole of the back of the hand and fingers. In a single case recorded by Turner 

 the posterior interosseous did not form the so-called ganglion behind the carpus, 

 but passed down to supply the adjacent sides of the index and middle fingers. 



DORSAL NERVES. 



These nerves are twelve in number, and, with the exception of the 

 larger part of the first of them, which joins the brachial plexus, they 

 are distributed to the walls of the thorax and abdomen. Eleven of the 

 nerves so distributed are termed intercostal, and the twelfth is situated 

 below the last rib. The cords connecting them with the sympathetic 

 nerve, placed close to the vertebras, are very short. 



The anterior divisions of these nerves pass separately to their destina- 

 tion, without forming any plexus by the connection or interlacement of 

 their fibres, and in this respect they differ from those of the other 

 spinal nerves. From the intervertebral foramina they are directed 

 transversely across the trunk, and nearly parallel one to another. The 

 upper six nerves, with the exception of the first, are confined to the 

 parietes of the thorax ; while the lower six nerves are continued fi-om 

 the intercostal spaces to the muscles and integument of the anterior 

 wall of the abdomen, 



FIRST DORSAL NERVE. 



The greater part of the anterior division of this nerve ascends over 

 the neck of the first rib and the first intercostal artery to enter into the 

 brachial plexus. The remaining portion of the nerve is continued as 

 the first intercostal, a small branch which courses along the first inter- 

 costal space, in the manner of the other intercostal nerves, but has 

 usually no lateral cutaneous branch, and may also want the anterior 

 cutaneous. 



UPPER OR PECTORAL INTERCOSTAL NERVES. 



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

 the intercostal blood-vessels. After a short space they pass between 

 the internal and external intercostal muscles, supplying them with 

 twigs, and, about midway between the vertebrae and the sternum, give 

 off the lateral cutaneous branches. The nerves, greatly diminished, 

 are now continued forwards amid the fibres of the internal intercostal 

 muscles as far as the costal cartilages, where they come into contact 

 with the pleura. In approaching the sternum, they cross the internal 

 mammary artery and the fibres of the triangularis sterni muscle. 

 Finally, these nerves pierce the internal intercostal muscle and the 



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