670 THE NERVOUS SYSTEM. 
the second or fourth sacral nerves, enter the pelvic plexus without being directly 
connected with the gangliated cord. These nerves, however, are to be regarded as 
homologous with the white rami communicantes of the thoracico-lumbar nerves 
(abdominal splanchnic). They convey to the pelvic viscera—(1) motor and 
inhibitory fibres for rectum, uterus, and bladder, (2) vaso-dilator fibres for the 
genitals, and (3) secretory fibres for the prostate gland. 
This portion of the cord is placed in front of the sacrum, internal to the anterior 
sacral foramina. It is connected above by a commissural cord with the lumbar 
portion of the sympathetic, and below it ends in a plexiform union over the coecyx 
with the cord of the other side, the two being frequently connected by the 
ganglion impar or coccygeal ganglion. ‘The number of ganglia is variable ; there are 
commonly four. They are of small size, gradually diminishing from above down- 
wards. 
Central communicating branches arise irregularly in the form of gray rami 
communicantes from the sacral ganglia, and join the anterior primary divisions of 
the sacral and cocecygeal nerves. 
Peripheral Branches of Distribution.—(1) Visceral branches of small size arise 
from the upper part of the gangliated cord, and pass inwards to join the pelvie 
plexus (see below). 
(2) Parietal branches, also of small size, ramify over the front of the sacrum, and 
form, in relation to the middle sacral artery, a plexiform union with branches from 
the ganghated cord of the other side. 
SYMPATHETIC PLEXUSES. 
It has already been seen that the peripheral branches of the sympathetic 
ganghated cord throughout its length are characterised by forming or joining 
plexuses i in their neighbourhood. 
The cervical sympathetic ganglia and nerves give rise to the carotid and 
cavernous plexuses; the external carotid, pharyngeal, thyroid, vertebral, and 
subclavian plexuses ; and they send important branches to the cardiac plexuses 
(described along with the pneumogastric nerve). 
The thoracic ganglia send branches to join the pulmonary and cesophageal 
plexuses (described along with the pneumogastric nerve). They form plexuses on 
the thoracic aorta, and “by means of the splanchnic nerves they form the chief 
source of the solar plexus. 
THE SOLAR AND PELVIC PLEXUSES. 
These great plexuses serve to distribute nerves to the viscera and vessels of the 
abdominal and pelvic cavities. ‘Taken together they include three plexuses—the 
solar plexus, hypogastric plexus, and the pelvic plexuses. They are constituted 
by peripheral branches of the lower thoracic, lumbar, and upper sacral parts of the 
gangliated cord of the sympathetic; and they are related to the central nervous 
system by means of the visceral branches (white rami communicantes) of the lower 
thoracic and upper lumbar nerves on the one hand, and by the visceral branches 
of the second and third, or third and fourth sacral nerves, on the other hand. The 
former series join the sympathetic cord, and reach the solar plexus through the 
splanchnic nerves mainly, to a lesser extent through the lumbar ganghated cord. 
The latter series enter the pelvic plexus without connexion with the sympathetic 
cord. The hypogastric plexus serves as a connecting link between the solar and 
pelvic plexuses. 
The solar plexus lies on the posterior abdominal wall behind the stomach. 
It is composed of three elements: the celiac plexus surrounding the origin of the 
coeliac axis between the crura of the diaphragm, and two semilunar ganglia, each 
lying on the corresponding crus of the diaphragm, and overlapped by the supra- 
renal capsule, and on the right side by the inferior vena cava. The plexus is 
continuous with subordinate plexuses, diaphragmatic, suprarenal, renal, superior 
mesenteric and aortic ; and by means of the hypogastric nerves the aortic plexus 
f ry 
