Integrative Systems 175 



tivity by hormones carried in the blood. From the fact that some vis- 

 ceral activities may be initiated and may proceed without stimulation 

 by nerves external to the organ, and the additional fact that most vis- 

 ceral organs possess intrinsic mechanisms which are adequate for main- 

 tenance of the basic or routine activity of the organ, it follows that, up 

 to a certain point, a visceral organ is autonomous. The numerous vis- 

 ceral ganglions and plexuses are the most peripheral (i.e., most remote 

 from the cerebrospinal system) elements of the autonomic nervous 

 system. 



A human community such as that of a town or city is autonomous 

 in the administration of most of its routine internal affairs. But in some 

 matters it is subject to control by the state or federal government. The 

 common welfare of the local community and the larger political whole 

 makes such control necessary. In the animal, each of the various parts 

 and the whole are mutually dependent and the parts are vitally de- 

 pendent upon one another. It is the somatic animal — the "outer tube" 

 that most directly meets the impact of agencies in the animal's outside 

 world. An outfit of autonomous visceral organs, each going its own way 

 and performing its routine function with inexorable uniformity, would 

 not serve the purpose. If the outer voluntary somatic animal is to make 

 effective reaction and adjustment to the vicissitudes of living, the vis- 

 ceral functions must be capable of prompt and appropriate regulation 

 to meet the ever changing requirements of the somatic animal. The 

 nervous mechanism which provides for this necessary correlation of vis- 

 ceral (in the broad sense of "visceral" — see p. 156) activities and their 

 regulation in relation to somatic activities consists of a complex system 

 of ganglions and connecting nerves interposed between the viscera and 

 the cerebrospinal system. This intermediating system has numerous 

 connections with the brain and spinal cord and is to be regarded as in- 

 cluding the intrinsic nervous mechanisms of the viscera themselves. In 

 its entirety it is known as the autonomic system (formerly com- 

 monly called "sympathetic"). In the following anatomic description, 

 some details refer particularly to mammals, whose autonomic system 

 is best known. In other vertebrates, the general arrangement of the 

 system is like that in mammals but with differences in details. 



Autonomic Ganglions 



The most conspicuous part of the autonomic system is a pair of 

 longitudinal nerve-cords lying just beneath the vertebral column and 

 close alongside and parallel to the dorsal aorta. The cords extend 

 throughout the regions of the trunk and neck, and into the base of the 

 tail in some vertebrates (Figs. 155, 156, 157). In the region of the trunk, 

 ganglionic enlargements occur at regular intervals along each cord. 



