1 6 OHIO STATE ACADEMY OF SCIENCE. 



I. Somatic Systems. 



1. Tactile, or general Cutaneous. 



2. Acustico-lateral, including nerves for lateral line organs (in the 



Ichthyopsida) and for organs of equilibration and hearing (in 

 vertebrates generally). These organs and their nerves have 

 probably been derived phylogenetically from the general 

 cutaneous system and, like the organs of the latter type, are 

 adapted for the reception of various kinds of mechanical 

 impact, either rhythmic or non-rhythmic. 



3. Visual (a system of uncertain relationship, provisionally classi- 



fied under the somatic sensory). 



4. Somatic motor, for the innervation of skeletal or voluntary 



muscles. 



II. Visceral Systems. 



5. Visceral sensory, unspecialized sensory nerves of the viscera, dis- 



tributed chiefly through the sympathetic nerves. 

 6- Gustatory, innervating specialized sense organs (taste buds) of 

 chemical sense, probably derived phylogenetically from the 

 preceding type. 



f. Olfactory (provisionally classified here because of the apparent 

 resemblance betwen taste and smell). 



8. Visceral motor, distributed chiefly to unstriped and involuntary 



muscles, generally through the sympathetic system. 



9. Excito-glandular, provisionally classified here because of general 



resemblance to the last mentioned type. 



There are numerous other systems which can be differen- 

 tiated physiologically, but which cannot as yet be completely 

 separated anatomically and classified, such as nerves for the 

 thermal sensations, muscle sensations, etc., but enough has been 

 done to enable us to lay down the general plan or pattern of the 

 peripheral nervous system as a whole and to define the main path- 

 ways by which stimuli of different modalities reach the brain and 

 are reflected back to the responsive organs. Our anatomical knowl- 

 edge of these pathways is sufficiently well controlled by precise 

 physiological experimentation to enable us to state with confidence 

 that each of the nine systems mentioned above is a real functional 

 unit. 



The fibers composing these systems may reach the central 

 nervous system through a series of many nerve roots arranged 

 in a segmental way, like the general cutaneous nerves of the 

 spinal cord, or they may all be represented in a single large 

 nerve, like the optic and olfactory. Thus it happens that some 

 nerves, like those last mentioned, are "pure" nerves, while others, 

 like the facialis or vagus, are "mixed," containing in some cases 

 as many as four anatomically distinguishable components. 



