172 PRINCIPLES OF VETERINARY SCIENCE 



brain from a frog. In such an animal all movements are pur- 

 poseful, but are without intelligent direction. The animal is 

 incapable of originating actions, but can perform reflex actions. 

 Thus, it may be said that the spinal cord converts afferent into 

 efferent impulses; it also serves as an independent nervous 

 center from which purposeful movements are originated. 



The functions of the sympathetic system are of two kinds: 

 First, it serves to transmit stimuli to the heart and other involun- 

 tary muscles and glands. Second, it conducts impulses from the 

 viscera to the cerebrospinal system under which it normally 

 works. In an emergency it has the ability to work independently 

 of the central nervous system to carry out peristaltic movements 

 in the hollow viscera. The sympathetic system is not to be 

 regarded as a separate nervous system but as an outlying part 

 of the cerebrospinal system, through which some fibers from 

 each spinal nerve pass on their way to the viscera. 



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