=Spinal Nerves.=--From the spinal cord arise the spinal nerves. Of these there are about thirty-eight pairs in the cat. Eight are =cervical=, thirteen =thoracic=, seven =lumbar=, three =sacral=, and seven or eight =caudal=. Those leaving the cervical (Fig. 133, 5-8 and _I_) and lumbar (Fig. 136) enlargements are larger than the others. The =first= cervical nerve leaves the vertebral canal through the atlantal foramen, the =second= leaves between the arches of the atlas and axis, while all the others leave the vertebral canal by way of the intervertebral foramina. Each nerve arises from the cord by a =dorsal= and a =ventral= root. The dorsal root is chiefly sensory, the ventral motor in character. The =dorsal= root (radix posterior) (Figs. 133, 135, and 136, _a_) begins as a number (twelve or more) of separate nerve-bundles which emerge from the posterior lateral groove. These roots lie nearly in a single plane and pass laterad, converging to penetrate a ganglion, the =spinal ganglion= (_b_) (or ganglion of the posterior root). All the spinal ganglia except the first and second are situated in the intervertebral foramina or within the vertebral canal. The first and second are situated among the muscles surrounding the place of exit of the nerves. The =ventral root= (radix anterior) (Fig. 135, _e_) arises as a larger number of small fibre-bundles which do not lie in a single plane, so that in a transverse section several rootlets may appear in a single section. The rootlets converge to form a single mass which joins the dorsal root just as it emerges from the spinal ganglion. The nerve formed by the junction of the ventral and dorsal roots is one of the =spinal nerves=. The direction in which the nerves leave the cord varies. In the cervical region (Fig. 133) and cranial part of the lumbar region it is nearly laterad; at the cervical and lumbar enlargements it is laterocaudad. The nerves in the sacral and caudal regions pass almost directly caudad to reach the intervertebral foramina and form thus a brush which surrounds the filum terminale (Fig. 136, _C_) and is called the =cauda equina= (Fig. 136, _B_). Each spinal nerve immediately after leaving the intervertebral foramen divides into two branches, a =dorsal= or =posterior= branch or =ramus= (_c_), and a =ventral= or =anterior ramus= (_d_). The dorsal ramus is in each case small (except in the first and second cervical nerves), and is distributed to the longitudinal muscles and integument of the back. The ventral rami are larger and each is connected a short distance beyond its origin with the sympathetic system by a short =ramus communicans= or communicating branch. Each is then distributed to the integument and muscles of the ventral part of the body, including the limbs. The ventral rami which pass to the limbs are much larger than the others. The ventral rami are further distinguished from the dorsal by the fact that they frequently unite with one another to form plexuses.