THE SPINAL CORD. 



659 



branches being apparently supplied Fl S- 173 - 



with sympathetic fibres from the 

 ganglia on their own posterior roots. 

 Some of these last fibres also pass 

 from the cerebro-spinal into the 

 Sympathetic system. By these 

 communications, the two systems 

 of fibres are so blended with each 

 other, that it is impossible to isolate 

 them. The branches proceeding 

 from the Semilunar ganglia are 

 distributed upon the abdominal 

 viscera; and those of the Cardiac 

 ganglia upon the heart and the 

 vessels proceeding from it. The 

 latter seem to accompany the arte- 

 rial trunks through their whole 

 course, ramifying minutely upon 

 their surface; and it can scarcely 

 be doubted that they exercise an 

 important influence over their func- 

 tions. What the nature of that 

 influence may be, however, will be 

 a subject for future inquiry. It is 

 so evidently connected with the ope- 

 rations of nutrition, secretion, &c., 

 that the designation of " nervous 

 system of organic life," as applied 

 to this system, does not seem objec- 

 tionable, provided that we do not 

 understand it as denoting the de- 

 pendence of these functions upon it. 

 Even in Vertebrata, however, we 



do not always find the distribution of the visceral trunks distinct from that of 

 the cerebro-spinal. In the Cyclostome Fishes, the par vagum supplies the 

 intestinal canal along its whole length, as well as the heart; and no appearance 

 of a distinct sympathetic can be discovered. In Serpents, again, the lower part 

 of the alimentary canal is supplied from the spinal cord, and the upper part by 

 the par vagum ; and though the lateral cords of the sympathetic may be traced, 

 they are almost destitute of ganglia. Even in the highest Yertebrata, some of 

 the glands, of which the secretion is most directly influenced by the condition 

 of the mind, are supplied with most of their nerves from the cerebro-spinal 

 system ; thus, the lachrymal and sublingual glands receive large branches from 

 the fifth pair, and the mammary glands from the intercostal nerves. 



2. Of the Spinal Cord and Medulla Oblongata ; their Structure and 



Actions. 



696. In our more detailed consideration of the functions of the several divi- 

 sions of the Nervous System, it is desirable, for several reasons, to commence 

 with the Cranio- Spinal Axis; which, as already pointed out ( 678), may be 

 considered as constituting the fundamental portion of this apparatus. The en- 

 tire Axis is divided into its Cranial and its Spinal portions, the passage of the 

 Cord through the foramen magnum of the occipital bone being considered 



Roots of a dorsal spinal nerve, and its union with 

 sympathetic : c, c. Anterior fissure of the spinal cord. a. 

 Anterior root. p. Posterior root, with its ganglion, a'. 

 Anterior branch, p'. Posterior branch, s. Sympathetic. 

 e. Its double junction with the anterior branch of the 

 spinal nerve by a white and a gray filament. 



