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DEVELOPMENT OF THE SYMPATHETIC SYSTEM. 673 
forwards on each side to form the cavernous plexus of the penis (plex. cavernosus 
penis). These nerves pierce the layers of the triangular hgament, and after 
supplying the membranous urethra at the root of the penis, give off branches which 
enter and supply the corpus cavernosum. The cavernous nerves communicate with 
branches of the pudic nerve, and give offsets to the corpus spongiosum and the 
spongy portion of the urethra. 
d. The uterine plexus passes upwards for a short distance with the uterine artery 
between the layers of the broad ligament, and is then distributed to the surfaces 
and substance of the organ. It communicates between the layers of the broad 
ligament with the ovarian plexus. 
The vaginal plexus is formed mainly by the visceral branches of the sacral 
nerves entering the pelvic plexus. It supplies the wall and mucous membrane 
of the vagina and urethra, and provides a cavernous plexus for the clitoris (plex. 
cavernosus clitoridis). The uterine and vaginal plexuses of the female correspond 
to the prostatic plexus of the male. 
DEVELOPMENT OF THE SYMPATHETIC SYSTEM. 
There are two diametrically opposite views of the mode of development of the sym- 
pathetic system. 
In birds and mammals the first rudiment of the sympathetic cord occurs in the 
formation of a longitudinal unsegmented column of mesoblastic cells (which stain more 
deeply than the mesoblast in which they lie) on 
either side of the aorta, and coterminous with it. 
This column of cells becomes joined at an early 
stage by the visceral branches of the spinal nerves 
which grow inwards from the main nerve trunks 
into the splanchnic area, and result from the 
division of the nerve into somatic and visceral 
parts. These visceral branches constitute the 
white rami communicantes. ‘They receive con- 
tributions usually from both dorsal and ventral 
roots, and gradually approaching the above-men- 
tioned column of mesoblastic cells, they become 
intimately associated with the cells. In some 
cases fibres of the visceral nerves pass over the 
cellular column into the splanchnic area without 
connexion with it (Fig. 483). By the junction of 
these visceral nerves with the cells of the column, 
certain cells persist and produce the ganglia. 
The intervening portions of the column, by 
changes in the cells, and by the addition possibly 
of fibres belonging to the visceral nerves, give 
rise to the commissural cords. The cellular 
column, besides producing the ganglated cord, 
by the further growth of its cells and their 
extension centrally and peripherally, produces the 
gray rami communicantes, parts of the peri- 
pheral branches, and the peripheral (collateral 
and terminal) ganglia, as well as the medullary 
portion of the suprarenal capsule. The cervical, 
lower lumbar, and sacral portions of the sympa- 
thetic gangliated cord are secondary extensions 
from the more primitive condition, gradually 
growing upwards and downwards along the main Fic, 482.—THr DEVELOPMENT OF THE 
vessels. These portions of the system are not SU ME SEI -GANGrAiEp (ORD. 
provided with white rami communicantes. The Sip sidaaeveny (alitenshntis| eoinihia 
ganglia of the sympathetic assume their segmented ones sali GaleVertebtal, eonionts =s1G, 
appearance (1) from the persistence of the primitive Dorsal ganglia. 
cells and their connexion with the spinal nerves 
by means of the white and gray rami communicantes, and (2) from the way in which the 
primitive column is moulded by the surrounding structures (bones, segmental arteries, etc.). 
A2 
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ae 
Sy, Sympathetic cord ; Spl, Splanchnic branches 
