THE SPINAL NERVES. 253 



The spinal nerves. The spinal nerves, arising from the spinal cord, 

 consist of thirty-one pairs, Fig. 60, arranged into five groups, named, 

 according to the vertebrae, between which they pass out from the spinal 

 canal, the cervical, dorsal, lumbar, sacral, and coccygeal nerves. There 

 are eight pairs of cervical nerves, twelve dorsal, five lumbar, five sacral, 

 and one, sometimes two, coccygeal. 



Each spinal nerve arises from the corresponding side of the spinal 

 cord, by means of two roots, which consist of bundles, or funiculi, 

 springing from the lateral furrows upon the cord. The deep paths of 

 these roots within the cord, require to be carefully studied. 



The funiculi which form the posterior root, larger arid more numerous 

 than those of the anterior root, arise from the posterior lateral furrow. 

 Within the cord, they may be traced into, or through, the posterior 

 white columns, whence they proceed either downwards, transversely, 

 or upwards, forming three sets. The descending set pass obliquely 

 downwards, through the gray matter, and even reach the anterior horn, 

 whence they penetrate the anterior white columns, spreading upwards 

 and downwards, many of them entering the anterior roots of the neigh- 

 boring nerves, but some losing themselves in the anterior columns. 

 The transverse set of fibres enter the posterior horn, crossing the ge- 

 latinous portion of this; some join the multipolar cells, others pass be- 

 tween them, either into the posterior or lateral columns ; others cross 

 through the transverse commissure of the cord, to reach the posterior 

 and lateral columns of the opposite side, some being traceable, it is 

 said, to the roots of the nerves : lastly, some end in a network reaching 

 towards the anterior cornua. The ascending set are partly continuous 

 with the fibres of the posterior columns, but most of them pass ob- 

 liquely upwards through these columns, and enter the gray substance, 

 where some appear to form loops, and return into the posterior 

 columns. 



The fibres of origin of the anterior roots, pass in distinct horizontal 

 bundles, through the anterior columns, to the anterior horn of gray 

 matter; thence they diverge in three directions, upwards, downwards, 

 and horizontally. Many may be traced to the large multipolar cells 

 of the anterior horn ; some pass through into the anterior, and others 

 into the lateral, white columns of the same side; others proceed through 

 the anterior part of the commissure, and pass over to the opposite side 

 into the anterior and lateral columns, and, it is said by some, even 

 into the anterior roots of that side ; many enter deeply into the cornua, 

 and then diverge upwards, downwards, and inwards; the latter come 

 into near proximity with the fibres of the posterior roots, and possibly 

 pass into them. 



On leaving the cord, the posterior funiculi are gathered into a single 

 nerve root, upon which is found an oval mass of gray matter, situated 

 usually in the intervertebral foramen, and called a spinal ganglion, or 

 ganglion of the posterior root of a spinal nerve. The anterior funiculi, 

 smaller and less regularly disposed, emerge in a similar manner from 

 the anterior lateral furrow. The anterior root, formed by the gather- 

 ing together of these funiculi, passes over, and beyond, the spinal gan-* 

 glion of the posterior root, and then joins that root to form a single 



