384 



DAVIDSON BLACK 



In the adult medulla of Rana catesbeana the most rostral 

 motor root of the IX-X series was taken to represent the motor 

 component of the IX nerve and has been so named in figures 3 

 and 9 A. It should be noted, however, that a well marked gen- 

 eral cutaneous component is to be observed entering the me- 

 dulla on the exit level of the motor IX root in figure 3. In this 

 respect the relations which obtam here would seem to differ 



Nu ac ''. 



Fig.- 3 Rana catesbeana. Transverse section through the medulla at the 

 exit level of the motor glossopharyngeal root. Abbreviations: Nu.ac.d., dorsal 

 acustic nucleus; Nu.o.s., s.uperior olive; Nu.IX.m., motor glossopharyngeal nu- 

 cleus; R. desc.V., radix spinalis trigemini; R.IX.m., motor glossopharyngeal root; 

 R.IX. s., sensory glossopharyngeal root; Tr.VIIL, area acustica alba; Vent. IV., 

 fourth ventricle. Other abbreviations as before. 



Fig. 4 Rana catesbeana. Transverse section through the medulla at the 

 exit level of the motor facial root. Abbreviations: Nu.ac.v., ventral acustic 

 nucleus; Nxi.VII.m., motor facial nucleus; R.VII.m., motor facial root; R.VII.s., 

 sensory facial root fibers; R.VIII., acustic root fibers. Other abbreviations as 

 before. 



from those described by Strong in larval forms, probably as the 

 result of a fusion of the roots which he has designated second and 

 third. 



The most caudal vagus rootlets in R. catesbeana are wholly 

 motor and emerge as fine strands to reach the periphery along a 

 line somewhat more ventrally placed than the line of emergence 

 of the rostral roots. " 



The motor X nucleus lies on the periphery of the periependy- 

 mal gray beneath the sulcus limitans in the caudal third of the 



