THE GREAT SYMPATHETIC NERVOUS SYSTEM. 893 



Afferent Branches. — Furnished by the inferior branches of the lumbar 

 nerves, tliese raujuscules comport themselves exactly like those of the dorsal region. 



Efferent Branches. — These are short filaments, analogous to those which, 

 by their union, constitute the splanchnic nerves. Their number is not constant, 

 and is generally less than that of the ganglia. Two or three join the lumbo- 

 aortic plexus ; the others reach the origin of the small mesenteric artery, anas- 

 tomose around it with the posterior extremities of the branches of that plexus, 

 and thus form another single network, designated the posterior mesenteric plexus 

 (Fig. 480, 18). 



This plexus, in the centre of which is a more or less voluminous ganglion, 

 sends to the various branches of the small mesenteric artery ramifications for the 

 walls of the small colon and the rectum. 



It supplies besides : 1. Two or three large branches which follow the posterior 

 mesenteric vein, and join the anterior mesenteric plexus, after throwing some 

 divisions into the colic mesentery (Fig. 480, 19). 



2. Satellite branches to the two spermatic arteries, constituting the plexus of 

 that name (Fig. 480, 20). 



.3. Two or three long divisions (Fig. 480, 21) which enter on each side of 

 the pelvis, by passing beneath the external face of the peritoneum, and reach 

 the lateral plane of the rectum, where they meet the filaments emanating 

 directly from the inferior sacral nerves. From the anastomosis of these divisions 

 results a rich nervous network, called in Man the hypogastric plexus, and which 

 we have designated the pelvic plexus ; this network supplies all the organs con- 

 tained in the pelvic cavity (Fig. 480, 23). 



5. Sacral Portion of the Sympathetic. 



A continuation of the lumbar cord, this portion of the sympathetic chain is 

 situated beneath the sacrum, to the inner side of the inferior sacral nerves. It 

 offers four very elongated ganglia, which communicate with these nerves by one 

 or more filaments, and which give rise to several very fine ramuscules that are 

 lost in the connective tissue on the inferior face of the sacrum. 



Its posterior extremity, which terminates behind the great sympathetic, does 

 not always comport itself in the same manner. We sometimes see it become 

 attenuated to a very delicate ramuscule, which passes on to the mesian coccygeal 

 artery, and anastomoses with that of the opposite side. But sometimes, also, 

 this ramuscule cannot be distinguished, and the sub-sacral cord seems to be 

 abruptly terminated by the filament of communication from the last sacral pair. 



Functions. — The functions of the sympathetic are as yet incompletely 

 known, notwithstanding the labours of many physiologists, at whose head must 

 be placed Claude Bernard. In a physiological condition, this nerve possesses 

 an extremely obscure sensibility, but which may, nevertheless, become very acute 

 in pathological states. It conveys to organs the unconscious, motor excitations 

 originating in the spinal cord or its ganglia ; and through the filaments it 

 furnishes to the vessels — the vaso-motor nerves — it holds under its control the 

 circulatoiy phenomena, especially in the capillary plexuses, causing these canals 

 to suddenly dilate or contract, and thus diminish or accelerate the flow of blood 

 in them. By this action on the blood-vessels, it may have a secondaiy influence 

 on the nutrition of the organs to which these vessels are distributed.^ 



' Francois Franck has published, in the Travaux du lahoratoire de M. Marey, pour VAnn€e 

 1875, a long memoir on the " Nerfs Vasculaires de la tete." The author passes in review the 

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