THE LATER DEVELOPMENT OF THE FROG 



211 



In the tadpole at this stage (shortly after hatching) there are 

 present also rudiments of parts of the visceral arches; the general 

 development of these will be described below, but it is necessary 

 to mention here one of these elements, the potato-quadrate, since 

 from the beginning it takes part in the formation of the cranium. 

 The paired palato-quadrate rudiments are formed as short, 



ct 



M 



pa 



mo 



FIG. 80. Dorsal views of the chondrocranium of the frog larva. A. Chondro- 

 cranium of a 7.5 mm. larva of R. temporaria. After Gaupp, from Stohr-Ziegler 

 model. B. Chondrocranium of a 14 mm. larva of R. fusca. After Gaupp, from 

 Ziegler model, a, Auditory capsule; bp, basal plate; c, notochord; ct, trabecular 

 cornu; /, basicranial fontanelle; in, inter nasal plate; ir, infrarostral cartilage; 

 3, jugular foramen (for IX and X cranial nerves); m, muscular process; M, 

 Meckel's cartilage; mo, mesotic cartilage; o, occipital process; pa, anterior ascend- 

 ing process of palato-quadrate cartilage; pi, parachordal plate; pp, posterior 

 ascending process of palato-quadrate cartilage; pq, palato-quadrate cartilage; 

 sr, suprarostral cartilage; t, trabecular cartilage. 



flattened, crescentic rods, lateral to the trabeculse. They 

 soon connect wdth the trabeculse by anterior ascending processes 

 a short distance back of the olfactory region, and by posterior 

 ascending processes opposite the extremity of the chorda. The 

 rudiments of the cranium thus marked out are now converted 

 into a continuous cartilaginous structure having the appearance 

 illustrated in Fig. 80, A . The large basi-cranial fontanelle in front 

 of the chorda is the seat of the infundibulum and pituitary body. 



