MOTOR NUCLEI IN PHYLOGENY 413 



(Ridewood, 49) by the fusion of the broad cerato-hyals with the 

 basi-hyal and hypobranchial elements.^ During larval life the 

 chief aspirator muscle is the diaphragmato-branchialis from 

 which is developed the sterno-hyoid muscle; but the most im- 

 portant levators of the bucco-pharyngeal floor are the mm. 

 orbito-hyoidei and sub-hyoidei which are innervated by nerve 

 VII (Schulze, 51). Thus during larval life, the muscles of the 

 hyoid arch are important inspiratory effectors while in the adult 

 this function is almost completely lost by the rearrangement 

 of these muscles. On account of this arrangement of the facial 

 musculature it is rather to be expected in view of the preceding 

 observations, that the VII and V motor nuclei in larval anurans 

 will not be so closely associated with one another as in adults of 

 this order, and it would not be surprising to find the motor 

 VII-IX-X nuclei associated in larval anurans in a manner very 

 similar to that obtaining in larval Amblystoma (v. Herrick, 

 I.e.). 



The oldest larval anuran material at present available to me 

 are 9 mm. tadpoles of Rana sp.? cut in series transversely at 

 6 micra. As none of this material is stained by Cajal or Golgi 

 methods no charts of the motor nuclear pattern can be recon- 

 structed with accuracy, but it can be determined with reasonable 

 certainty that the motor VII nucleus of the 9 mm. frog tadpole 

 lies relatively further caudad of the motor V nucleus than in 

 any adult anuran examined. In the tadpole the distance be- 

 tween the motor V and VII nuclei is greater than the total 

 length of the motor V nucleus itself. Strong's observations (53) 

 would also indicate that the nucleus of origin of the motor VII 

 root is differently arranged in the tadpole than in the frog. 

 This author describes a motor root which emerges at the most 



^ According to Ridewood (1. c.) the development of this region in Pelodytes 

 is in general very similar to that obtaining in other tadpoles. In the 13 mm. 

 Pelodytes the ceratohyals and basihyal (basibranchial) together with the hypo- 

 branchial plates form a ventro-median complex from which the distal ends of 

 the ceratohyals and the bar-like ceratobranchials radiate outwards. This com- 

 plex by the fusion of its elements forms in the 23 mm. larva a structure which 

 in its shield-like arrangement is essentially similar to the adult anuran basilin- 

 gual plate. 



