408 DAVIDSON BLACK 



breathing members of the group while in adult anurans, though 

 also exclusively air breathing forms, an essentially different 

 type of visceral motor nuclear pattern is evident. If Gaupp's 

 conclusion be correct, a typically anuran nuclear pattern should 

 begin to be manifest in these forms early in ontogeny and the 

 circumstances combining to produce this pattern must likewise 

 have arisen early in larval life.* With this in view it will be 

 of interest to inquire whether or not any correlation is evident 

 between the arrangement of the bucco-pharyngeal effector 

 mechanism and that of the motor nuclei from which it receives 

 its innervation, 



Motor V nucleus. The position of the motor V nucleus with 

 reference to the exit level of its root is subject to relatively 

 little variation among amphibians. In anurans the motor V 

 nucleus is relatively larger than in urodeles and its cells are 

 more easily distinguished from the neighboring tegmental 

 elements, 



Reflex connections both crossed and direct are evidently 

 established between the motor and sensory nuclei of the V 

 nerve on the level of the entrance of the latter, and Herrick 

 (29) has shown further that in Amblystoma, individual fibers 

 of the mesencephalic V root send collaterals into the homolateral 

 motor V nucleus. Herrick's observations would indicate that 

 this relation of the mesencephalic V root to the motor V 

 nucleus is an important one for proprioceptive reflexes of the 

 head muscles. 



The muscles innervated by the trigeminal nerve in the am- 

 phibians under discussion are as follows: in Rana, mm. ptery- 

 goideus, temporalis, masseter, submentalis and submaxillaris ; 

 in Siren, mm. pterygoideus, temporalis, masseter, intermandibu- 

 laris anterior and posterior, anterior part of the m. inter- 

 hyoideus and in addition, two small muscles which hav& been 

 termed by Norris the levator and retractor muscles of the ant- 



' It may be recalled again in this connection that in the 38 mm. Amblystoma 

 larva, a tj^pical urodele visceral motor nuclear pattern is already evident, al- 

 though at this stage the motor VII nucleus is not in direct continuity with the 

 motor IX-X (v. fig. 10, also Herrick, 29, fig. 1). 



