394 



DAVIDSON BLACK 



DISCUSSION 



1. Hypoglossal complex 



In the foregoing description of the nucleus of the second 

 spinal nerve in R. catesbeana, and in the subsequent comparison 

 of the morphology of this area in anurans and urodeles, one 

 very striking feature became apparent, viz.: that in all opistho- 

 glossal anurans examined there is developed a very well cir- 

 cumscribed dorso-medial cell group in the rostral end of the 

 cervical somatic motor column, while in all urodeles examined 

 no such circumscribed nucleus is to be distinguished in this 

 area. 



In an enquiry into the significance of the difference in the 

 development of this cell group in the members of these two am- 

 phibian orders, it is necessary to consider first whether or not 

 the plan of peripheral distribution of the motor fibers of the 

 first two spinal nerves is fundamentally different in anurans and 

 urodeles. In this connection Rana is taken as representative 

 of opisthoglossal anurans. Triton, Siren, and Cryptobranchus 

 have been selected among urodeles because in these forms the 

 motor nuclei have been studied from the point of view of the 

 present investigation and reconstruction charts are available 

 for comparison (fig. 10). 



Fig. 9 Reconstruction charts of motor roots and nuclei in anurans. A, Rana 

 catesbeana; B. R. esculenta (after Kappers) ; C, R. fusca (after Rothig) ; D, Bufo 

 (after Rothig). Abbreviations: Yl, abducens roots; IX, motor glossopharyn- 

 geal root; X, motor vagus root; Xll, most rostral cervical somatic motor rootlet 

 (hypoglossus). The arrow indicates the site of the calamus. See diagram 

 above for explanation of signs. 



