626 NERVOUS SVSTEM 
ventral muscles between the pelvis and tail, together with those of 
the cloacal region and the copulatory organs. 
The dorsal branches of all the spinal nerves in the whole pelvic 
region are restricted to small, cutaneous branches in conformity with 
the reduction of the dorso-spinal muscles. The caudal nerves are 
also small, their dorsal branches supply the levator and their 
ventral the depressor muscle of the tail. 
Ul. The Cranial or Cerebral Nerves have been already described 
(BRAIN). 
IV. The Sympathetic System consists of the visceral branches of 
the Cerebro-Spinal Nerves, and supplies chiefly the alimentary and 
genital organs and the circulation. ‘The Nerves composing it have 
no axial cylinder: they are paler than the white fibres, and are 
characterized by the presence of ganglia in their course, each 
branch containing one near its base which beside sending off 
other ramifications is connected with the corresponding ganglion of 
the next metamere, so as to form a “Sympathetic” chain running 
along each side of the ventral surface of the vertebral column. 
The two chains by means of these connexions somewhat resemble 
a ladder, the cross-bars of which are called rami communicantes, 
from a mistaken notion that they join the longitudinal “ strand” 
or ». sympathicus of their side with the medulla, the fact being 
that the cross-bars are the true “rests,” the lateral strands rather 
making the connexion between the successive ganglia. In the 
region of the NECK each of these strands runs, accompanied by 
the vertebral artery of its side, through the transverse foramen of 
each of the cervical vertebrae. In the thoracic region each strand 
is double, and the basal ganglia are successively connected with the 
next by a nervous branch which runs over the head of the rib, and 
by another which passes directly through the space between the 
head of the rib and its tubercle. In the pelvic region each strand 
again becomes single; but, conversely to the single strand of the 
cervical region, each is composed of ventral branches only, while 
lastly in the caudal region the right and left branches approach 
and coalesce in the middle line. From the first thoracic ganghon 
there issues a cardiac branch supplying the HEArt, while other 
branches starting from neighbouring ganglia form a sort of plexus 
which, accompanying the cceliac artery, innervate the stomach, LIVER 
and other viscera. Similar branches from the basal ganglia of the 
lumbar and sacral regions form a plexus with ganglia numerously 
. interspersed, and serve the rest of the Alimentary Canal, the 
KIDNEYS (page 480), genital organs and CLoaca (page 90), where 
they partly anastomose with the branches of the Pudic portion of 
the Sacral Plexus. 
From the first pair of cervical ganglia the Sympathetic strands 
are continued on either side to the ganglia of the n. hypoglossus, 
