662 THE NERVOUS SYSTEM. q 
THE SYMPATHETIC NERVOUS SYSTEM. 
The sympathetic nervous system consists of a pair of elongated gangliated 
cords (nervi sympathici), extending from the base of the skull to the coecyx ; con- 
nected, on the one hand, by a series of branches to the spinal nervous system, and 
on the other hand giving off an irregular series of branches to the viscera. At its 
cephalic end each sympathetic cord is continued in a plexiform manner into the 
eranial cavity along with the internal carotid artery, and forms complex relation- 
ships with certain cranial nerves. At their caudal ends the two sympathetic 
cords become joined together by fine filaments, and are connected by the coceygeal 
ganglion (g. impar). ) Tee 
The sympathetic system (1) serves to rearrange and distribute fibres derived 
from the cerebro-spinal system to the viscera 
and vessels of the splanchnic area; (2) it trans- 
mits to the cerebro-spinal system afferent fibres 
from the viscera; and (3) it transmits fibres to 
the vessels, involuntary muscles and glands, in 
the course of the somatic divisions of the spinal 
nerves. 
General Structure of the Sympathetic 
System.—The sympathetic system is composed 
of two elements—gangha and nerve fibres. 
The ganglia (g. trunci sympathici) are 
variable in number, form, size, and position. 
They are not definitely segmental in position, 
but they are always connected together by a 
system of narrow commissural cords of nerve 
fibres. A ganghon consists of a larger or 
smaller number of multipolar nerve-cells, en- 
closed in a capsule of connective tissue. Each 
——___ SPLANCHNIC a‘ 2 2 
FY errerent Gell is provided with one avon and a number of 
os dendrites. The axon may enter into the com- 
position of (a) the commissural cord; (0) 
SSS sreancue central branch (gray ramus communicans); or 
! aves" (e) a peripheral branch from the sympathetic 
Bie) $/5.— SCHEME OF THE CONSTITUTION OF Gord. ‘These axons are commonly, medulllaned 
THE WHITE RAMUS COMMUNICANS OF THE ; ee : 
Sear at their origin, but become non-medullated in 
The roots and trunks of a spinal nerve are their course from the parent cell. Besides 
shown, with the white ramus passing be- these gangha, two other series of ganglia are 
tween the’ spinal nerve ‘anda. sympatheue “oresent in! veonnexion “with the sqpem plans 
ganglion (Sy). The splanchnic efferent ; ; ; 
fibres (in red) are shown, partly ending branches of the sympathetic,—intermediate or 
in the ganglion, and partly passing ie collateral ganglia, on the branches or in the 
yond the ganglion into a peripheral brane te sympathetic plexuses and terminal ganglia, i 
The splanchnic afferent fibres (in blue) are ~¢ 3 ? : 
shown, partly entering the ganglion, and Close relation to the endings of the nerves in 
passing upwards or downwards in the the viscera. 
gangliated cord ; partly passing over the 
cord into peripheral branches. 
The nerve fibres in the sympathetic system 
are of two classes, medullated and non-medul- 
lated. The distinction is not absolute. The medullated fibres may lose their 
medullary sheaths before reaching their terminations; and the non-medullated 
fibres may at their origin possess a medullary sheath. The medullated fibres 
form the series of white rami communicantes (the visceral branches of the 
spinal nerves). They take origin from the anterior primary divisions of certain 
spinal nerves in two streams, thoracico-lumbar from the first (or second) thoracic 
to the second or third lumbar nerve, and pelvic, or sacral, from the third, 
and second or fourth sacral nerves. The roots of these nerves arise from both 
dorsal and ventral roots of the spinal nerves, but in largest numbers from the 
ventral root. The fibres from the ventral root are of very small size. They are 
the axons of nerve-cells within the spinal cord, and passing through the white 
ramus, they enter the sympathetic cord, and end by forming arborisations around 
waa 
