254 SPECIAL PHYSIOLOGY. 



trunk, which, passing out from the intervertebral foramen at the side 

 of the vertebral column, divides into anterior and posterior branches, 

 which are distributed, the latter to the muscles and skin behind the 

 spine, and the former to the muscles and integuments of the parts of 

 the body in front of the spine, and to the limbs; the anterior branches 

 are accordingly generally larger; moreover, they form plexuses, as will 

 be presently mentioned, and they are all connected by branches with 

 the sympathetic nerve. 



The upper cervical nerves supply the deep and posterior muscles, 

 and the skin of the neck and shoulder. From the anterior branches 

 of the third and fourth cervical nerves, with a small fasciculus from 

 the fifth, a most remarkable branch, called the phrenic nerve, runs 

 down through the thorax, on the sides of the pericardium, and reaches 

 the diaphragm, or partition between the thorax and abdomen, to the 

 muscular fibres of which it is distributed. The lower cervical nerves 

 which arise from the cervical enlargement of the cord, and are much 

 larger than the upper cervical, are chiefly distributed by the large 

 anterior branches, to the muscles, the skin, and other parts of the 

 upper limbs, a few branches being furnished to the neck and trunk. 

 The dorsal nerves give off, besides some small branches to the upper 

 limb, the intercostal nerves, which supply the proper muscles of the 

 thorax, namely, the intercostal muscles, the deep muscles of the back, 

 the upper part of the muscles of the abdomen, and the skin over the 

 corresponding parts of the trunk. The first dorsal nerve assists in 

 supplying the upper limb. The lumbar nerves supply the lower part 

 of the muscles of the back and abdomen, the muscles within the pelvis, 

 and the muscles and skin of the lower part of the trunk, of the upper 

 part of the thigh, and the skin of the inner side of the thigh and leg, 

 down to the heel. The first lumbar nerve is sometimes joined by a 

 branch from the last dorsal, whilst the fourth partly, and the fifth 

 almost wholly, descends to join the large upper sacral nerves. The 

 sacral nerves chiefly supply certain muscles of the pelvis, those of the 

 back of the thigh, all those of the leg and foot, and the parts of the 

 skin of the lower limb, not supplied from the nerve already mentioned. 

 The two lower lumbar, and the three upper sacral, nerves arise from 

 the lumbar enlargement, and are the largest of the spinal nerves, and 

 indeed larger than any of the cranial nerves, being the largest nerves 

 in the body. The coccygeal nerves, the smallest of the entire series, 

 supply the parts adjacent to the coccyx. 



The roots of the cervical nerves within the spinal canal, are short, 

 arise at brief intervals from the sides of the cord, and pursue a nearly 

 horizontal course to the interspaces, or places of exit, between the 

 vertebrae; but, in the dorsal region, the roots of the spinal nerves are 

 longer and more oblique; and, on arriving at the lumbar and sacral 

 nerves, as the spinal cord itself- terminates opposite the lower border 

 of the first lumbar vertebra, the roots of the nerves spring in a crowded 

 manner from the cord, and, descending in the vertebral canal, inclosed 

 within the sheath of the cord, pursue a progressively longer and 

 more vertical course, before they reach their respective intervertebral 

 .foramina of exit. The pointed lower portion of the spinal cord, to- 



