178 ANATOMY OF VERTEBRATES. 



and the extensor digitorum, whilst a long branch passes on and 

 gives filaments to the extensors of the pollex and to the wrist- 

 joint, but does not terminate on this part in a ganglion, as in Man 

 and Quadrumana. 



There are thirteen pairs of dorsal nerves, and their principal 

 deviation from those in Man consists in a smaller size, a more 

 direct course, and a less distribution on the abdominal muscles, 

 and by those at the lower part of the thorax being covered 

 by an extension of the origin of the psoas muscle, also in the 

 anterior cutaneous branches supplying the different portions 

 of the elongated mammary glands in the female, as well as the 

 skin. The posterior or dorsal divisions, after supplying the 

 muscles connected with the spine, the sacro-lumbalis and longissi- 

 mus dorsi, send a branch between these and the latissimus dorsi 

 to the skin. The anterior or ventral divisions of the lumbar and 

 sacral nerves supply principally the parts connected with the 

 lower extremity, the bladder and rectum ; the dorsal divisions of 

 the second and third lumbar nerves supply the skin as well as the 

 sacro-lumbalis and other muscles connected with the dorsal parts 

 of the vertebrae ; the dorsal divisions of the succeeding lumbar 

 nerves are distributed to the muscles only ; the dorsal divisions of 

 the sacral nerves supply the muscles on that surface of the tail. 

 The nerves are not very different from those in Man, except in 

 their number, and consequently in their conjunction a little 

 higher or lower for forming the nerves of the lower extremity. 

 The anterior divisions of the three first lumbar nerves give fila- 

 ments to the psoas muscle, and then pass forward to terminate in 

 the abdominal muscles and skin. The fourth gives filaments to 

 the psoas and internal iliac muscles, and sends a branch to join 

 one from the third to form the external spermatic on the external 

 iliac artery, which passes through the external abdominal ring to 

 the spermatic chord ; in the female this was distributed on the 

 posterior division of the mammary gland ; it sends off another 

 branch which gives a filament to the external iliac artery, and 

 then joins the sixth; the rest of the fifth passes down on the 

 exterior of the thigh to the skin, and forms the external cutaneous 

 nerve. The sixth receives a branch from the fifth, gives fila- 

 ments to the internal iliac muscle ; part of it is then joined by a 

 large branch from the seventh to form the anterior crural nerve ; 

 the other part, after receiving a large and small branch from the 

 seventh, becomes the obturator nerve. The seventh, having 

 given off the preceding branches, joins the first and second sacrals 

 and a branch of the third for forming the sciatic nerve. The 



