418 



VERTEBRATE LIFE AND ORGANIZATION 



Glossopharyngeal 

 andvagLts 



■Aortic arches 



commun.ica.ns 



Splanchnic nerve 



/ 



Coeliaco mesenteric 

 artery 



/ 



Dorsal aorta 

 / 

 Sympathetic cord 



Urostyle 



Figure 21.19. A ventral view of the spinal nerves and sympathetic cord lying on 

 the right side of the vertebral column. (Modified after Gaupp.) 



nerves, together with certain of the motor fibers in several of the cranial 

 nerves, constitute a special part of the peripheral nervous system known 

 as the autonomic nervous system. The autonomic system, which in- 

 nervates visceral organs, blood vessels and glands, will be considered 

 more fully later. 



The nervous system receives impulses from the sense organs, in- 

 tegrates them, and sends out impulses to appropriate effectors. This is 

 often accomplished by simple reflexes— stereotyped, subconscious re- 

 sponses to specific stimuli. For example, when one pinches the toe of a 

 frog, a sensory neuron carries the impulse into the spinal cord. Here it 

 is transferred by a short connector neuron (or perhaps directly by the 

 sensory neuron) to a motor neuron that transmits it to the leg muscles, 



