54 NERVOUS SYSTEM A^D GENERAL SENSATION. 



[ 114. " If we agree, then, that the sympathetic in general 

 performs the functions of the cerebro-spinal nerves at large, we 

 must still admit that it exhibits numerous peculiarities. It not 

 only extends over all the vegetative organs of the abdomen, 

 and in part also of the thorax, but, by its fibrils detached 

 from the ganglia, it accompanies the great blood-vessels in their 

 course, and with these penetrates every part of the body. In 

 its motory, as well as hi its sensitive functions, it also exhibits 

 essential modifications : the motions of the parts to which it is 

 distributed are abstracted from the empire of the will. These 

 involuntary, and in the healthy state, unconscious, motions, 

 extend to the most remote structures with which it is in com- 

 munication, by means of ganglia, such as the iris, for example. 

 Reaction upon stimulation generally lasts longer than the sti- 

 mulus, which is exactly the reverse of what happens in refer- 

 ence to the muscles of voluntary motion, when the reaction so 

 constantly ceases before the stimulus is removed. The sensi- 



*- 



bility, as already observed, is extremely slight in the healthy 

 state. The conduction from the peripheral to the central parts, 

 has therefore undergone a manifest alteration, and even partial 

 interruption, as it would seem. The central parts receive no 

 impressions from the organs which are supplied with nerves 

 from the sympathetic ; and they have, farther, no power of 

 controlling the motions of these organs. These remarkable 

 effects can only be referred to the influence of the ganglions."*] 

 [ 115. The nervous system of the articulata is arranged dif- 

 ferent from, that of the vertebrata. The absence of an internal 

 osseous skeleton in the former removes the nervous centres into 

 new relations : and accordingly, we find it associated with the 

 tegumentary and muscular systems, and ruled by the law which 

 regulates their development. We still, however, distinguish 

 cerebro-spinal, and sympathetic nerves. The brain is situated, 

 without exception, above the anterior extremity of the digestive 

 tube, and connected by two lateral trunks with the spinal 

 cord. Instead of being situated in the dorsal region of the body, 

 as in the vertebrata, it is found, on the contrary, without ex- 

 ception, along the abdominal line. This difference in the dispo- 

 sition of the nervous system constitutes one of the essential 

 characters distinguishing the two great primary subdivisions 



* Wagner's Physiology, p. 512, et seq. 



