MOTOR NUCLEI IN PHYLOGENY 405 



the relative development of the fasciculus solitarius and its as- 

 sociated gray in urodeles and anurans. 



It it be difficult to determine whether the communis area is 

 relatively more highly developed in one amphibian group than 

 in the other, then this would appear to indicate that the pres- 

 ence of additional taste buds within the mouth area of urodeles 

 as compared with anurans cannot be of very great functional 

 importance. But a large number of visceral sensory fibers must 

 enter the fasciculus solitarius which are not concerned in gus- 

 tatory conduction, and it is conceivable that the impulses they 

 conduct should also exercise an influence on the reflex action of 

 the musculature innervated by the motor VII-IX-X nerves 

 a^nd thus be important factors in determining the motor nuclear 

 pa^ttern. 



In general it may be said that the extent of the peripheral 

 area inervated by the communis components of the VII-IX-X 

 nerves among metamorphosed amphibians varies directly with 

 the number of persisting gill clefts. In adult anurans, in the 

 adult Cryptobranchus japonicus and in all the adult Salaman- 

 dridae, gill clefts are lacking, so that in these forms the area in- 

 nervated by general visceral sensory fibers should be approxi- 

 mately equal. On this basis of reasoning, the representation 

 of these fibers within the fasciculus solitarius should also be 

 approximately equal in the animals mentioned, and appreci- 

 ably less than among perennibranchiate forms. One might 

 expect, if the influence of these communis fibers upon the reflex 

 action of the VII-IX-X musculature and consequently upon 

 the motor VII-IX-X nuclei be in proportion to their numeri- 

 cal representation within the communis area, that such a con- 

 siderable reduction in their number would lead to some alter- 

 ation of motor nuclear pattern away from the type obtaining 

 in perennibranchiate amphibians. Since both Cryptobranchus 

 japonicus and Triton exhibit the typical urodele motor pattern 

 after metamorphosis is complete, it becomes evident that in 

 determining this pattern the simple numerical representation of 

 the general visceral sensory components in the communis 

 area cannot be an important deciding factor, though the greater 



