THE NERVOUS SYSTEM 



535 



the lumbar and sacral vertebrae, are drawn out into a bundle of nerves 

 parallel to the spinal cord and lying within the spinal canal. From its 

 resemblance to a horse's tail, this is known as the Cauda equina. Similar 

 relations are found in anura and in some teleosts. 



THE AUTONOMIC NERVOUS SYSTEM 



In the higher chordates a special system of nerves, the autonomic, is 

 distributed to the smooth muscles of the digestive and circulatory systems 



I Clarke's column 



S0MAT1C.<A^„-H 

 MOTOR 

 GANGLION, 

 CELLS 



M_50MATIC 

 ■^ MUSCLE 



VISCERAL MOTOR 

 FIBERS 



Fig. 442. — A diagram of neurons of the spinal cord and spinal nerves shown in their 

 relations to one another and to their end-organs. Somatic sensory fibers are shown by 

 continuous lines, somatic motor fibers by fine dots. Visceral sensory fibers are indi- 

 cated by short broken lines, visceral motor by long broken lines. (Redrawn after 

 Plate.) 



and to many other organs. This autonomic system is most evident in the 

 chain of S3nnpathetic ganglia which lie along the dorsal aorta from the 

 neck to the sacrum. These, however, are only a portion of the autonomic 

 system, which is distinguished by functional rather than anatomical 

 characteristics, for the cerebrospinal system is so intimately connected 

 with autonomic nerve fibers that the two systems cannot be separated 



