72 DAVtDSON BLACK 



Nerve V 



In Damonia the motor V root arises in a dorsally situated 

 large-celled nucleus and its emergent fibers course in a direct 

 manner lateroventrad to reach the periphery of the brain stem 

 ventral to the entering sensory V root as in Rana (fig. 6). The 

 chief bulk of the nucleus lies on the level of its root exit, a small 

 portion only extending rostrad of this plane and none of its cells 

 being found below the level of the caudal border of its emergent 

 root (fig. 11 C). 



In figure 6 the motor V root is seen to be separated by a slight 

 space from the more dorsally placed incoming fibers. Among 

 the latter may be distinguished the mesencephalic V root which 

 pursues its course from this level to its nucleus of origin in the 

 midbrain in a manner essentially similar to that already described 

 by Van Valkenburg in Chelone (39 and 41). The mesencephahc 

 V root in Chelydra has also been figured though not described 

 by Humphrey (28, pi. Ill, fig. 21), who refers, however, to 

 Herrick's earher description of this root in reptiles (24, p. 138). 



As in Chelone, the caudal part of the motor V nucleus in 

 Damonia is most ventrally situated, though no indication of an 

 isolated ventral motor V nuclear moiety is to be seen in the latter 

 form. Damonia differs from Chelone, however, in the smaller 

 relative size of its motor V nucleus and in the rostral position 

 of this nucleus with reference to Ihe exit level of the motor V 

 rootffig. ll,CandD). 



The arrangement of the cells of the motor V nucleus in Alligator 

 resembles in general that in Chelone. In Alhgator (fig. 12, A), 

 however, this nucleus is much more caudally placed with refer- 

 ence to its root exit and the ventroperipheral moiety is more 

 distinct than in Chelone. In Boa and Varanus (fig. 12, B and 

 C) a still more extensive development of the ventroperipheral 

 portion of the motor V nucleus is evident, and no part of the 

 nucleus in these forms occupies such a dorsal position as does 

 the chief bulk of the motor V cell group in Alligator (Kappers, 

 31,32). 



