138 



NERVOUS SYSTEM OF VERTEBRATES. 



of the first evidences of the development of coordinating functions 

 on the part of the cerebellum, which was originally a simple 

 general cutaneous center. 



The distribution of the root fibers of the acustico-lateral system 

 of nerves to the- special cutaneous nuclei in the medulla oblongata 

 and cerebellum of fishes is shown in Fig. 69. This figure should 

 be compared with that for the general cutaneous centers (Fig. 

 59). The central tracts from the special cutaneous centers in 

 fishes are identical with those from the general cutaneous centers. 



In aquatic amphibia and in the tadpoles of land forms the 



L . lineae lateralis 



funic. 



N. l.l.VII 



-^-:--::dXII " 

 N. lineae lateralis 



Fig. 69. — A diagram to show the central endings of the special cutaneous com- 

 ponents in fishes. 



acustico-lateral system has essentially the same relations as in 

 fishes. In terrestrial forms, however, the pit organs disappear 

 because they are serviceable only in the water. Only the enclosed 

 canals of the ear with their sense organs persist. In reptiles, 

 birds and mammals also, the inner ear is the only representative 

 of this system of sense organs which holds so prominent a place 

 in fishes. In mammals the VIII nerve is divided into two parts, 

 the N. vestibularis and the N. cochlearis, and for these nerves 

 two sets of nerve centers have been developed from the acusticum 

 of fishes. The vestibular nerve suppKes the sense organs in 



