no 



PHYSIOLOGY. 



Fig. 29. 



Each of these systems thus mingles with the other, the cerebro- 

 spinal transmitting both 

 motor and sensitive fibres 

 into the sympathetic ; 

 whilst the sympathetic is 

 represented in the cere- 

 bro-spinal system by cer- 

 tain fibres and collections 

 of vesicular matter of its 

 own. (Fig. 29.) 



Adopting this view of 

 the compound nature of 

 the sympathetic, it seems 

 to be impossible to re- 

 gard it either as inde- 

 pendent of the cerebro- 

 spinal centres, or wholly 

 depending upon them. 

 It is probably indepen- 

 dent of them as regards 

 its gelatinous fibres, but 

 dependent upon them as 

 regards its tubular fibres. 

 It is to be looked upon 

 as a portion of the ner- 

 vous system, peculiar in 

 its composition, having, 

 as regards some of its 

 constituent fibres, a spe- 

 cial relation to the blood-vessels, especially the arteries, but being by 

 its other fibres connected with the cerebro-spinal centres. It is also 

 distributed both to sentient surfaces and to muscles, as to the heart 

 and intestinal canal, movements in which can be excited by stimu- 

 lation of the ganglia connected with them. The well-known occur- 

 rence of pain in parts supplied by it, proves the existence of sensitive 

 fibres. 



The sympathetic thus appears to exercise a threefold office : 

 first, that of a sensitive nerve to the parts to which it is distributed ; 

 secondly, that of a motor nerve for certain muscular parts ; and 

 thirdly, that of a nerve to the blood-vessels. By the last arrange- 

 ment it may influence nutrition and secretion by its effect upon the 

 contractility of the coats of the vessels. The effect of the emotions 



lat * ^'^" ^^* ^oote of a dorsal spinal nerve, and its union wiUi tlie sj'mpathetic. c. c. An- 



-'or fissure of the spinal cord. a. p. Anterior and posterior roots, s. Sympathetic, cits 



9'ZO. ''' junction with the anterior branch of fhe spinal nerve, by a white and a gray 



