2IO NERVE COMPONENTS OF BONY FISHES. 



theless it must not be forgotten that independently of that 

 the size of these nerves will be determined largely by the 

 relative development of the different parts of the head. 

 Thus in the selachians the development of the rostrum, 

 which is undoubtedly a dorsal region, has necessitated a 

 large increase in the general cutaneous nerve supply. In 

 such teleosts as Menidia, on the other hand, the dorsal 

 surface ^of the head over and in front of the eyes has been 

 reduced to a minimum, with a corresponding loss in the 

 nerve supply. 



XII. — Comparison with Acipenser and Lota. 



We have in our discussion of the nerve roots earlier in 

 this section called attention to the failure of Goronowitsch's 

 segmental scheme of the trigemino-facial nerves ('88 and 

 '96, especially the latter). He arranges, it will be recalled, 

 the trigemino-facial roots in three homodynamous series, 

 each with dorsal sensory and ventral motor roots, (i) tri- 

 geminus I (my general cutaneous and motor V roots), (2) 

 trigeminus II (my two lateralis roots), (3) facial (my com- 

 munis and motor VII). In this very attractive scheme 

 there are two fatal defects. The first is that the ventral 

 root of his trigeminus II is sensory, not motor. The sec- 

 ond and more radical difficulty arises out of the fact that 

 Goronowitsch considers disparate structures to be serially 

 homologous. Thus, of the three dorsal roots in question 

 which he considers to be homologous with each other and 

 with^the spinal dorsal roots, the first is general cutaneous, 

 the second fis lateralis and the third is communis. Now, 

 it is of course possible that future researches may show 

 that this root complex represents two or three or more 

 primary metameres; but the origin and distribution of 

 these root fibres in the adult certainly negative any such 



