190 Journal of Comparative Neurology. 



ascending V, which associate themselves with that tract near 

 the exit of the nerve. The cells among which these fibers 

 appear presumably represent a terminal nidus, the sensory nidus 

 of Osborn. Its extent in Nectiirus is much less however than 

 in CryptobrancJms. 



(3). Motor nidus. A short distance cephalad of the level 

 shown in Fig. 19 the motor nidus of the fifth nerve appears in 

 the floor of the metencephal, succeeding, but entirely separated 

 from the nidus of the seventh, compared with which it is much 

 more compact. It extends cephalad to the exit of the nerve. 

 From this two bundles of fibers pass down to constitute the 

 smaller roots of the fifth, V^+^, which however, fuse immedi- 

 ately with the larger root. 



(4). From the Mesencephal. As stated by Osborn, the 

 large ganglion cells in the roof of the mesencephal which con- 

 stitute the mesencephalic trigeminal nidus, are quite numerous 

 in Necttiriis. They are found scattered throughout the extent 

 of the roof but are massed more closely just cephalad of the 

 cerebellum, as described by Osborn (Fig. 22). From this 

 nidus large fibers spring which pass caudad grouping themselves 

 in two divisions, one of which enters and passes ventrad through 

 the cerebellum ; most of these fibers enter the large root (V^) 

 of the nerve. Others pass the fifth without entering it, as 

 noted by Osborn, and may be traced caudad, meso-dorsad of 

 the ascending V, to the neighborhood of the seventh and 

 eighth nerves. 



The two smaller roots of the trigeminal are evidently not 

 entirely the same as the motor root of man, inasmuch as from 

 the latest evidence the mesencephalic descending tract enters 

 the smaller motor root in man. Nor, indeed, would V^ and V^ 

 in Necturtts be the same as the rootlets in CryptobrancJms, which 

 Osborn found to be formed by the descending tract. 



/, //, ///, and IV. — The remaining cranial nerves have 

 received but superficial attention, and little more can be said of 

 them than that their origins seem to be as described in other 

 Amphibia. 



The trochlearis (IV) is very small in Necturus, and I failed 



