No. I.] THE CRANIAL NERVES OF AMPHIBIA. 173 



connected with bipolar ganglion cells. Principally distributed 

 to mucous canals. 



Root III. — Non-m9tor, " hintere." Only fine fibres. Large 

 ganglionic masses. Distributed especially to mucous mem- 

 branes, skin, and touch organs, especially on the barbels. 



Root IV. — Exclusively motor, arising close in front of the 

 Acusticus and going over into the VII (coarse-fibred). 



The numbers vary owing to subdivisions and fusions. 



According to Stannius the Facialis proper (Hyoideo-mandi- 

 bularis) divides into a posterior, or more caudal branch, the R. 

 hyoideus, and a more anterior one, the R. mandibularis, pro- 

 ceeding along the lower jaw, which either gives off a branch to 

 the mucous membrane of the mouth or subdivides into a R. 

 mandibularis externus to the skin and mucous canals, and a R. 

 mandibularis internus to the mucous membrane of the mouth. 



In the first account (Pleuronectes), root i, evidently, is the 

 Trigeminus proper, 2 and 3 are the lateral line roots, and 5 the 

 motor root. Root 4, probably, is the one described by Stannius 

 elsewhere and by other authors as arising from the lobus 

 trigemini. The question of its homologue in Amphibia will 

 be discussed below. There is, however, some obscurity in 

 Stannius' account of this root. It would appear from his 

 description to lie sometimes ventral and sometimes {e.g., com- 

 pare his account of Cyprinoids) dorsal to 2 and 3. 



Gegenbaur (26) describes, in Hexanchus, the Trigeminus as 

 arising fronj two trunks, an anterior and a posterior one 

 (" vordere " V« and " hintere " N b). The former is composed 

 of two roots with difficulty distinguishable. The posterior 

 trunk is also composed of two roots, one, the most dorsal (V a) 

 arising from a large swelling overhanging the fourth ventricle, 

 and the other more ventral (V/S) emerging from the medulla 

 close above the Facialis, and somewhat cephalad and dorsad 

 to the Acusticus. N b proceeds above \ a and the two enter 

 the Gasserian ganglion, there being an intermingling of fibres. 

 The R. ophthalmicus is derived principally, but not exclusively, 

 from Va. 



Jackson and Clarke (32) describe the Trigeminus as arising 

 in Echinorhinus from two main trunks. (i) V a, furthest 



