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INTRODUCTION TO NEUROLOGY 



ing to water vibrations of slow frequency and probably assisting 

 in the orientation of the body in space. These are the lateral 

 line canals. They are innervated by special roots of the VII and 

 X pairs of cranial nerves (the lateralis roots of these nerves), 

 which are drawn in black in Figs. 43 and 44. The other nerves 

 are lightly shaded or white. The lateral line organs and their 

 nerves are entirely absent in higher vertebrates (see p. 199). 



The lateral line nerves and the acoustic nerve (VIII pair) in 

 fishes terminate in a common center within the brain (the acous- 

 tico-lateral area), which is shaded with horizontal cross-hatch- 

 ing in Figs. 43 and 44. The nerves of general cutaneous sen- 

 sibility also terminate in a particular region which is unshaded 



Optic lobe 



Epithalamua 



Thalam 



Supra-orbital trunk 



Acoustico-lateral area 

 Gang, lateralis VII 



Hypothalam 



Ganglion V 

 Infra-orbital trunk 



hi 



r. hyomandibularis VII 



Spiracle 



r. palatinus VII 



Ganglion geniculi VII 



Fig. 44. The same brain as Fig. 43 seen from the side and slightly enlarged. 



and marked "general cutaneous area." The visceral nerves 

 from the gills, stomach, etc., all enter a single "visceral area," 

 which is shaded with vertical lines. The eye is also connected 

 with a special region in the midbrain, the "optic lobe," which is 

 shaded with oblique cross-hatching; and the nose is connected 

 with a part of the forebrain which is stippled. 



We may, therefore, recognize in this fish a "nose brain," an 

 "eye brain," an "ear brain," a "visceral brain," and a "skin 

 brain," each of these peripheral organs having enlarged primary 

 terminal nuclei which make up definite parts of the brain sub- 

 stance. Remembering that the primitive brain was a simple 

 tubular structure, we observe that each one of the chief sense 

 organs and each group of similar sense organs sends sensory 



