78 DAVIDSON BLACK 



interval must intervene between the caudal end of the oculo- 

 motor group and the rostral end of the trochlear nucleus in this 

 form. 



In the oculomotor nucleus of Hatteria, Gisi has described both 

 dorsofrontal and ventrocaudal cell groups (20, p. 176). Further, 

 she has noted that most of the caudal fibers of the oculomotor 

 root in this animal arise in the contralateral ventral nucleus of 

 this nerve. 



DISCUSSION 



1. Hypoglossal complex 



In the preceding description it has been noted that differen- 

 tiation within the hypoglossal nuclear area in Damonia, Chelone, 

 Alligator, Boa, and Varanus has not reached a stage much in 

 advance of that obtaining in opisthoglossal anurans. 



Among the latter forms it has been shown that the differ- 

 entiation of the hypoglossal cell group is definitely correlated 

 with the development of the tongue as a muscular prehensile 

 organ (5). In view of this, a relatively slight differentiation of 

 the hypoglossal nuclear area might be expected in Alligator and 

 in chelonians, since the tongue of these animals is non-protrusible. 

 In Varanus, on the other hand, lingual movement is not so re- 

 stricted, and in Boa the tongue is modified to form a highly 

 specialized tactile organ. In neither of these forms, however, 

 does the morphology of the hypoglossal nucleus show evidence 

 of a higher state of differentiation than that obtaining in Alligator. 



It is of interest to recall that the arrangement of the occipito- 

 spinal nerve roots in reptiles is on a plan more primitive than 

 that obtaining in the Anura. In adult opisthoglossal anurans 

 the first occipitospinal nerve ('a' of Fiirbringer's table, 16) is 

 missing and the fibers arising in the dorsomedial cell groups or 

 XII nucleus of these forms are restricted in their exit to one 

 ventral root, viz., that of the second spinal nerve ('b') of Fiir- 

 bringer's, first of the adult series). On the other hand, all the 

 roots of Fiirbringer's occipitospinal series are represented in the 

 reptiles under discussion so that the fibers arising in the rostral 

 portion of the somatic motor column (dorsal cell group or hypo- 



