No. I.] THE CRANIAL NERVES OF AMPHIBIA. 



97 



It is also evident that the lateral-line system has no especially 

 segmental character, and that it cannot properly be used in the 

 manner in which it has been attempted to use it, as a general 

 guide in determining the segmentation of the head. 



4. Motor Component. 



The fourth, motor component, shall not be treated here at 

 length. In all the forms above the Cyclostomes we have 

 splanchnic motor roots to the V, VII, IX, and X. 



Ahlborn describes no such roots, apparently, except for the 

 V, where it is very large. As Julin (33) and Dohrn (15) assert 

 that the VII has motor elements, it is possible a motor root 

 will yet be found for it. Ransom and Thompson (50) describe 

 large motor fibres, which unite with the Vagus in Petromyzon, 

 but not in Myxine. These fibres, however, are from anterior 

 roots. There are, besides, exceedingly fine fibres to the heart 

 and blood vessels. 



It would appear, both judging from this and from the con- 

 ditions in the tadpole, that a distinction exists between vaso- 

 motor and branchio-motor nerves, though both are considered 

 visceral. 



The following are these motor roots in the authorities 

 mentioned above : 



