782 



THE NERVES. 



Fig. 361. 



owes its chain-like aspect ; they are usually elliptical m shape, though they 

 may also be round or semilunar ; in all cases they are studded with prolonga- 

 tions'at their borders. Beneath each of the regions of the spine they are equal 

 in number to the vertebrae, with the exception of the cervical region, in 

 which 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 con- 

 stituted ; 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 sympathetic 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 speaking, they have neither origin 

 nor terminations they are always giving off branches 

 which are as frequently replaced by others ; in this way 

 they might be compared, in this respect, to the median 

 spinal artery, which offers somewhat the same ^mode of 

 constitution with its afferents supplied by the spinal 

 branches from the intervertebral foramina, and its efferents 

 destined to the substance of the spinal medulla. 



STRUCTURE. The ganglia of the great sympathetic 

 differ but little in their structure from the spinal ganglia, 

 whose constitution has been already made known. 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 gan- 

 glia; they are round, or furnished with poles that bring* 

 them into communication with the afferent and efferent 

 GAN- nerve-tubes ; there are also, in the ganglia, tubes which 

 A only pass through it, and merely lie beside the cells. 



The afferent branches of the ganglia have the white tint 

 o f ^he cerebro- spinal nerves, and are named the grey 

 nerves. They owe their colour to the fibres of Remak, 

 which they contain in large quantity. With these 

 nucleated fibres are associated fine nerve-fibres, and 



SYMPATHETIC 

 GLION FROM 

 PUPPY. 



a, a, Trunk of the 

 sympathetic nerve ; 

 6, Communicating 

 branches from a 

 spinal nerve ; these 

 divide into two fas- 

 ciculi which pass 

 upwards and down- 

 wards in the trunk ; 

 c, c, The 



composed of gan- 

 glion cells ; d, Small 

 branch, probably 

 destined to accom- 



are 



double-contoured fibres which proceed from the com- 

 municating rami, or afferent filaments supplied by the 

 spinal nerves ; these fibres often leave the ganglia to 

 ganglion pass directly to organs. 



In describing the sympathetic chain, it is divided into 

 five sections : a cephalic, cervical, dorsal, lumbar, and 

 sacral. 



pany an artery ; 

 Visceral branch. 



1. Cephalic Portion of the Sympathetic. 



This is composed of the spheno-palatine, ophthalmic, 

 and otic ganglia, all of which communicate with the superior cervical 



