1354 



HUMAN ANATOMY. 



the glandular tissue and {b) 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 neurones. 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 

 Fig. 1 129. . a complex of spinal and sym- 



pathetic fibres intermingled 

 with groups of ganglion-cells. 

 The activating path, which 

 proceeds from the nerve cells 

 of the spinal cord to end 

 somewhere around a sympa- 

 thetic neurone, constitutes a 

 preganglionic fibre and connects 

 the gray matter of the spinal 

 cord with the sympathetic 

 ceil. The continuation of the 

 path to the involuntary 

 muscle is formed by a second 

 link, the postganglionic fibre, 

 which conveys the impulse 

 from the sympathetic neurone 

 toward its destination in in- 

 voluntary muscle. Hence, a 

 preganglionic fibre carries an 

 impulse from the spinal cord 

 toward the sympathetic neu- 

 rone, while a postganglionic 

 fibre carries the impulse away 

 from the sympathetic neurone. 

 The postganglionic fibres are 

 the chief components of the 

 splanchnic efferents. 



Other postganglionic 

 fibres, those destined for the 

 supply of the involuntary 

 muscle of the outlying (so- 

 matic) blood vessels, hair fol- 

 licles and skin, have a different 

 cotirse, since they are axones 

 of the sympathetic cells of the 

 ganglipted cord, which pass, as 

 the gray ramicommunicantes, 

 to become incorporated with 

 the spinal nerves and dis- 

 tributed by them to the so- 

 matic areas of the body. The 

 paths formed by the pre- and post-ganglionic fibres are all motor tracts. In 

 addition to these, the splanchnic efferents contain a number of visceral afferents 

 that pass along the sympathetic strands, without connecting with the neurones, 

 until they reach their presiding cells within the' spinal ganglia and enter along the 

 posterior spinal roots to seek their reception nuclei. 



In order to provide for the outlying tracts of invoiuntary muscle contained 

 within the blood vessels outside the body-cavaties and within the skin, the sym- 

 pathetic fibres join by way of the gray rami communicantes, the somatic spinal 

 nerves, which they accompany to all regions of the body. 



Diagram showing constitution of sympathetic system; spinal 

 efferents are black ; sympathetic efferents are red; sympathetic (vis- 

 ceral) afferents are blue; SC, spinal cord; AR, PR, anterior and 

 posterior root of spinal nerve ; SG, spinal ganglion ; AD, /'Z?, anterior 

 and posterior primary divisions; IVR, GR, whjte and gray rami 

 communicantes. GC, gangliated cord ; SvG, sympathetic ganglia ; 

 CG, cervical sympathetic ganglion; PvG, SiibG, Tj-G, prevertebral, 

 subsidiary and terminal ganglia; SpE/, splanchnic efferents; SoE/, 

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



