1354 



HUMAN ANATOMY. 



FIG. 1129. 



the glandular tissue and () in consisting of at least two, sometimes of more, links be- 

 tween the source of the impulse (the spinal cord) and the structure upon which it is 

 expended. It is these interposed links that constitute the sympathetic elements 

 proper the sympathetic iit'itronrs. The cell-bodies of these neurones exhibit a 

 marked disposition to become aggregated into larger or smaller collections, which 

 constitute the innumerable ganglia that form a conspicuous feature of the sympathetic 

 system, whilst their axones serve to connect the ganglia with the terminal structures 

 (muscles or glands) or with other neurones. It is evident, therefore, that the 



sympathetic system consists of 

 a complex of spinal and sym- 

 pathetic fibres intermingled 

 with groups of ganglion-cells. 

 The latter are, for the most 

 part, stellate in form and pro- 

 vided with axones which, while 

 often pursuing a long course 

 as splanchnic efferenis, acquire 

 only partially or not at all a 

 medullary coat and hence may 

 be classified usually as non- 

 medullated fibres. Since the 

 spinal fibres are provided with 

 this covering, the bundles of 

 such fibres present the whitish 

 color distinguishing medullated 

 strands, in contrast to the gray- 

 ish tint of the strands of the 

 nonmedullated sympathetic fila- 

 ments. It is upon this histolog- 

 ical variation of their predomi- 

 nating fibres that the difference 

 recognized in the white and 

 gray rami communicantes, pres- 

 ently to be described, depends. 

 Although the supply of the 

 thoracic, abdominal and pelvic 

 organs constitutes an important 

 part 1 of the duty of the sympa- 

 thetic nerves, it is by no means 

 their entire concern, the inner- 

 vatic >n of the involuntary muscle 

 of the vessels and of the skin 

 and the glands throughout the 

 body being likewise their task. 

 In order to meet their obliga- 

 tions to the structures within 

 the body cavities, the sympa- 

 thetic nerves naturally follow 

 the course of the blood-ve>sels, 

 with the result that every artery 

 of consequence within these re- 

 gions is surrounded by a more or less elaborate net-work, these plexuses in most 

 l>Mring the names of the arteries which they accompany. In order to provide 

 for the outlying tracts of involuntary muscle contained within the blood-vessels outside 

 the body-cavities and within the skin, as well as for the glands, the sympathetic fibres 

 join, by way of the gray rami communicantes, the somatic spinal nerves, which 

 they accompany to all parts of the body. For this reason the peripheral somatic 

 nerve-trunks coiuain three varieties of fibres afferent and efferent spinal and efferent 

 sympathetic. 



Diagram showing constitution of sympathetic system ; spinal 

 efferents are black ; sympathetic efferents are red ; i\ mpattietic (vis- 

 cenl) afbrentt are blue; SC, spiiuil ond; -IA', /'A', anterior and 

 posterior root of spinal nerve ; SG, spinal ganglion ; AD, /^anterior 

 and posterior primary divisions; It 'A', (,'A\ white and gray rami 

 communicantes. CC, gangliated cord ; SyG, sympathetic ganglia; 

 CG, cervical sympathetic ganglion; PvG, StibG', Tr(,'. prevertehval, 

 subsidiary and terminal ganglia; Spfy, splanchnic efferents; SoEf, 

 somatic efferents ; V, vessels of the spinal meninges; /.intestine. 



