THE SPINAL NERVES 811 
which there is a gray nodular enlargement, the spinal ganglion (Ganglion spinale). 
Beyond the ganglion the dorsal root joins the ventral root to constitute the nerve. 
The ganglia are external to the dura mater, and are situated in the intervertebral 
foramina, except in the case of the sacral and coccygeal nerves, the ganglia of which 
lie within the vertebral canal. Those of the coccygeal nerves are intradural. 
The ganglia vary greatly in size; that of the first cervical nerve is scarcely as large as a hemp- 
seed, while that of the eighth cervical is about 2 cm. long and 1 cm. wide. On the large roots 
connected with the cervical and lumbar enlargement of the cord there are multiple ganglia of 
varying sizes interposed in the course of the root-bundles. The fibers of the dorsal roots arise 
from the cells of the spinal ganglia; connected with each ganglion cell there is a process which 
bifurcates, giving rise to a fiber which enters the spinal cord and another which passes into the nerve. 
The ventral root (Radix ventralis) contains fewer fibers than the dorsal root, 
except in the case of the first cervical nerve. It arises from the ventral surface of 
the spinal cord (Fig. 626) by means of numerous small bundles of fibers which do 
not form a linear series, but emerge from the cord over an area three to five 
millimeters in width (ventral root zone). The fibers are processes of the 
large cells of the ventral gray 
columns of the spinal cord. Spinal branch of intercostal artery 
There is no ganglion on the 
ventral root. 
In the cervical, thoracic, and 
anterior lumbar regions the bundles 
of both roots pass through separate 
openings in linear series in the dura 
mater before uniting into a root 
proper. Further back the bundles 
of each root unite within the dura. 
In the anterior part of the cervical 
region and in the thoracic part of the 
cord there are intervals of varying 
length between adjacent roots, but in , 
some places the fibers of adjacent 
roots overlap and an exchange of 
fibers may be observed. Many of the 
roots are directed almost straight out- 
ward or incline slightly backward, but 
the posterior lumbar, sacral, and coc- 
cygeal roots and nerves run backward Conjugal ligament 
to reach the foramina, through which 
they emerge. The distance thus to Fic. 651—Verresrar Canat OreNnep BY SAWING OFF THE ARCHES, 
be traversed increases from before (After Schmaltz, Atlas d. Anat. d. Pferdes.) 
backward, so that these nerves form 
a tapering sheaf around the conus 
medullaris and filum terminale in the last lumbar vertebra and the sacrum, which is known as the 
cauda equina. 
Spinal ganglion 
Dura mater 
Lig. denticulatum 
== Dorsal root bundles 
Dorsal longitudinal ligament 
The size of the spinal nerves varies greatly. The largest are connected with 
the cervical and lumbar enlargements. 
In, or immediately after its emergence from, the intervertebral foramen each 
spinal nerve gives off a small meningeal branch (Ramus meningeus). This is 
joined by a bundle of fibers from the ramus communicans and enters the vertebral 
eanal, in which it is distributed. Each nerve then divides into two primary 
branches, dorsal and ventral (Ramus dorsalis, ventralis). The dorsal branches 
are smaller than the ventral, except in the cervical region. They are distributed 
chiefly to the muscles and skin of the dorsal part of the body. The ventral branches 
supply in general the muscles and skin of the ventral parts of the body, including 
the limbs. Each nerve or its ventral branch is connected with an adjacent ganglion 
of the sympathetic system by at least one small short branch known as a ramus 
communicans. Many nerves have two and some have three such rami. A nerve 
may be connected with two ganglia, and a ganglion may be connected with two 
nerves. 
