886 



THE NERVES. 



As has been already shown in the general consideration of the nerves and 

 the whole nervous system, this apparatus has for its base two long cords extend- 

 ing from the head to the tail, underneath the vertebral column, and to the right 

 and left of the mesian line. Towards the last sacral vertebra, a portion of these 

 two cords converge towards each other, and lie beside the mesial coccygeal 

 artery. Some anatomists think that the great sympathetic does not stop at this 

 point, but is prolonged beneath the coccygeal vertebrte, where it enters a gan- 

 glion that has been described of late years as the " coccygeal gland " {Luschka's 

 gland) ; this, however, is not a nerve-ganglion. 



Each cord presents on its course numerous ganglia, to which it owes its 

 chain-like aspect ; they are usually elliptical in shape, though 

 they may also be round or semilunar ; some are studded with 

 prolongations at their borders. Beneath each of the regions 

 of the spine, these ganglia are equal in number to the 

 vertebrae, with the exception of the cervical region, in which 

 there are only two — one at the top, the other at the bottom, 

 of the neck. 



To this chain arrive afferent branches, by the union of 

 which it is constituted ; these branches are furnished by the 

 nerves of the medulla oblongata and the inferior spinal 

 branches, except those of the coccygeal region. The afferent 

 branches join the sympathetic at each ganglion ; but as there 

 are only two ganglia in the region of the neck, the afferent 

 filaments of the cervical nerves are grouped in such a manner 

 as to reach the superior and inferior ganglion. 



Those nerves which are given off from the ganglia to be 

 distributed to the viscera, are named the efferent or emergent 

 branches. They are interlaced around the arteries to reach 

 their destination, forming plexuses on the surface of these 

 vessels. 



This general idea of the disposition of the great sym- 

 pathetic is sufficient to show that its double ganglionic chain 

 does not represent two particular nerves arising at one 

 determinate point, and ending at another. Properly speak- 

 ing, they have neither origin nor termination ; they are 

 always giving off branches, which are as frequently replaced 

 by others. In this way they might be compared to the median 

 spinal artery, which offers somewhat the same mode of con- 

 stitution — with its afferents supplied by the spinal branches 

 from the intervertebral foramina, and its eff'erents destined to the substance of 

 the spinal cord. 



Structure. — The ganglia of the great sympathetic differ but little in their 

 structure from the spinal ganglia, which have been already described. They 

 have an envelope of connective tissue, which sends very fine septa into their 

 interior. In the spaces are cells a little smaller and paler than those of the 

 spinal ganglia ; they are round, or furnished with poles that bring them into 

 communication with the afferent and efferent nerve-tubes ; there are also, in the 

 ganglia, tubes which only pass through it, and merely lie beside the cells. 



The afferent branches of the ganglia have not the white tint of the cerebro- 

 spinal nerves ; they are named the grey tierves. They owe their colour to the 



SYMPATHETIC GAN- 

 GLION FROM A 



puppy. 



a, a. Trunk of the 

 sympathetic nerve ; 



b, communicating 

 branches from a 

 spinal nerve; these 

 divide into two fas- 

 ciculi which pass 

 upwards and down- 

 wards in the trunk; 



c, c, the ganglion 

 composed of gan- 

 glion cells; c?, small 

 branch, probably 

 destined to accom- 

 pany an artery ; e, 

 visceral branch. 



