No. I.] THE CRANIAL NERVES OF AMPHIBIA. 169 



sight it would be naturally suggested that the root coming 

 from the lobus trigemini, the dorsal root of Trigeminus II, is 

 represented in Urodela by the upper of Osborn's two Facial 

 roots, i.e., "VII u'' This, however, I believe is not the case. 

 As has been mentioned, both VII '' u" and "/" together 

 probably correspond to the dorsal VII in the tadpole, as is also 

 shown by Amblystoma. Furthermore, the root from the lobus 

 trigemini is fine-fibred, and though Osborn mentions that the 

 fibres of VII « are smaller than those of VII /, yet the differ- 

 ence is slight and both are coarse-fibred. From my own 

 observations, and from such investigations as those of Gas- 

 kell and others, I am inclined to believe that the size of the 

 fibres is more constant, and consequently of more importance in 

 determining homologies than would at first sight be supposed. 



Before looking further for the homologue of the lobus tri- 

 gemini in Amphibia, a glance will be taken at the condition in 

 the Teleosts. In the teleostean medulla oblongata, as is well 

 known, there are three greatly hypertrophied portions known 

 usually as the lobus vagi, the lobus trigemini, and the tuber- 

 culum acusticum. Mayser (41) speaks of the common origin 

 of the Acusticus and R. vagi lateralis, and is so much impressed 

 by it that he terms the latter a posterior acoustic root and, 

 further, considers the sense organs supplied by the latter as an 

 accessory auditory organ. He also quotes Leydig, to show the 

 similarity between the semicircular canals and their ampullae 

 and the mucous tubes of the lateral line. Speaking of the 

 same organs on the head he says: " Auch diese Schleimrohren 

 haben nach Stannius nur breite Nervenfasern und zwar aus der 

 II Wurzel des Trigeminus. Die II Ouintuswurzel des Stannius 

 entspringt aus dem Tuberculum acusticum und ist bei den 

 Cyprinoiden, wie jener Autor, p. 28, sagt, 'fast ganz verdeckt 

 von der III Wurzel,' d. h. unserer dorsalen geknieten " (= root 

 from lobus trigemini). From this the homology of the tuber- 

 culum acusticum with the centre in the medulla of the dorsal 

 VII and N. lateralis of the tadpole, and with the " dorso-lateral 

 Strang " of Goronowitsch in Acipenser is quite evident. 



According to Goronowitsch, Trigeminus II gives off the 

 following branches : R. ophthalmicus superficialis, R. buccalis, 



