198 STRONG. [Vol. X. 



It must be remembered, however, as shown above, that there 

 is reason for believing these roots, except those in Crypto- 

 branchus and Protopterus, are in reality compound, and include 

 a component from the fasciculus communis (lobus vagi). 



The motor root and the fasciculus communis root forms, as 

 we have seen, the constant part of the Facialis, including the 

 portio intermedia, which persists in the higher vertebrates. It 

 is, of course, this motor root which becomes so much more 

 important in the highest forms owing to the development of 

 the facial musculature. 



5. Comparison with the Cyclostomes. 



It will be well to take a glance at the conditions among 

 Cyclostomes, which, probably, present very primitive condi- 

 tions, and which should throw much light upon the origin of 

 the various differentiations existing among the cranial nerves 

 of the higher fishes. There have been many contradictory 

 statements made, however, concerning the Cyclostome periph- 

 eral nervous system, and I think it will be evident that our 

 knowledge of it is still far from accurate. 



Langerhans (40) describes two kinds of cutaneous sensory 

 organs. One is situated in papillae, which are especially 

 numerous around the mouth and on the dorsal "fin," but are 

 also found scattered over the body and in the mouth and 

 pharynx. The other is situated at the bottom of pits, and 

 these pits are arranged irregularly in lines, there being a line 

 above and a line below the gills, other lines proceeding along 

 the side of the body, above the middle; and still other lines 

 around the mouth and over the head, around the eye. These 

 sunken organs he homologizes with the lateral-line system. 



According to Ahlborn (i and 2), the Trigeminus springs 

 from the medulla by three roots, one above the other. The 

 most dorsal is the ophthalmicus, and arises from the ascending 

 trigeminal tract. It has a separate ganglion. The next is the 

 remainder of the sensory Trigeminus, and has the same origin. 

 The most ventral motor root arises from the motor trigeminal 

 nucleus and a descending tract. The ascending Trigeminus is 



