5 ?6 SPINAL NERVES. 



passes down between the superficial and deep layer of muscles, to the middle of 

 the forearm. Considerably diminished in size, it descends on the interosseous 

 membrane, beneath the Extensor secundi internodii pollicis, to the back of the 

 carpus, where it presents a gangliform enlargement, from which filaments are 

 distributed to the ligaments and articulations of the carpus. It supplies all the 

 muscles of the radial and posterior brachial regions, excepting the Anconeus, 

 Supinator longus, and Extensor carpi radialis longior. 



DORSAL NERVES. 



The Dorsal Nerves are twelve in number on each side. The first appears 

 between the first and second dorsal vertebrae, and the last between the last dorsal 

 and first lumbar. 



The roots of origin of the dorsal nerves are few in number, of small size, and 

 vary but slightly from the second to the last. Both roots are very slender ; the 

 posterior ones exceeding in thickness those of the anterior only in a slight degree. 

 These roots gradually increase in length from above downwards, and remain in 

 contact with the spinal cord for a distance equal to the height of, at least, two 

 vertebrae, in the lower part of the dorsal region. They then join in the inter- 

 vertebral foramen, and, at their exit, divide into two branches, a posterior or 

 dorsal, and an anterior or intercostal branch. 



The first and last dorsal nerves are exceptions to these characters. 



The posterior branches of the dorsal nerves, which are smaller than the intercostal, 

 pass backwards between the transverse processes, and divide into external and 

 internal branches. 



The external branches increase in size from above downwards. They pass 

 through the Longissimus dorsi, corresponding to the cellular interval between it 

 and the Sacro-lumbalis, supplying these muscles, as well as those by which they 

 are continued upwards to the head, and the Levatores costarum ; the five or six 

 lower ones giving off cutaneous filaments. 



The internal branches of the six upper nerves pass inwards to the interval 

 between the Multifidus spinaB and Semi-spinalis dorsi muscles, which they supply; 

 then, piercing the origin of the Khomboidei and Trapezius, become cutaneous 

 by the side of the spinous processes. The internal branches of the six lower 

 nerves are distributed to the Multifidus spinaB, without giving off any cutaneous 

 filaments. 



The cutaneous brandies of the dorsal nerves are twelve in number, the six 

 upper being derived from the internal branches, and the six lower from the ex- 

 ternal branches. The former pierce the Rhomboid and Trapezius muscles, close 

 to the spinous processes, and ramify in the integument. They are frequently 

 'furnished with gangliform enlargements. The six lower cutaneous branches 

 pierce the Serratus posticus inferior, and Latissimus dorsi, in a line with the 

 angles of the ribs. 



INTERCOSTAL NERVES. 



The Intercostal Nerves (anterior branches of the dorsal nerves) are twelve in 

 number on each side. They are distributed to the parietes of the thorax and 

 abdomen, separately from each other, without being joined in a plexus, in which 

 respect they differ from all the other spinal nerves. Each nerve is connected with 

 the adjoining ganglia of the sympathetic by one or two filaments. The intercostal 

 nerves may be divided into two sets, from the difference they present in their dis- 

 tribution. The six upper, with the exception of the first, are limited in their 

 distribution to the parietes of the chest. The six lower supply the parietes of 

 the chest and abdomen. 



The UPPER INTERCOSTAL NERVES pass forwards in the intercostal spaces with 

 the intercostal vessels, lying below the veins and artery. At the back of the chest, 



