90 



INTRODUCTION. 



eye and perforates the lower eyelid ; the intestiue 

 shortens ; the anal tube ceases to function, and dis- 

 appears with the last vestiges of the caudal crest, 

 which had become detached from the vent; and the 

 __ young frog, usually still bearing a stumpy tail, leaves 

 fV__^e water. The metamorphosis is completed. 



The skull and its appendages also undergo very 

 important changes. The cranium in the tadpole is a 

 large undivided cartilage with narial openings and 

 large suborbital fenestra. The suspensorium of the 

 lower jaw is extremely elongate, and sends up a 

 strong process, connected with the ci'anium by a 

 bridge, in front of the eye. The prsemaxillaries are 



Fig. 37. 



■pro 



pro 





A. Skull of full-grown tadpole of Peioiaies/iisctts. B. The same 

 at the end of the metamorphosis, after the loss of the horny 

 beak. chij. Oeratohyal cartilage, eo. Exoccipital. f'p. Pronto- 

 parietal. II. Lower labial cartilage, me. Mandibular (Mecke- 

 lian) cartilage, na. Nasal processes of chondrocranium. po. 

 Prasorbital process, 'pro. Prootic. su. Suspensorium (palato- 

 quadrate). ul. Upper labial cartilage. 



represented by a single or paired cartilage, the upper 

 labial, loosely attached to the diverging anterior pro- 

 cesses of the cranium, which supports the upper horny 

 beak; and to this corresponds a pair of cartilages, 

 the lower labials, ultimately the mento-Meckelian or 

 symphysial bones, supporting the lower beak and 

 attached to the short mandibular or Meckelian 

 cartilage. In the transformation of the mouth this 

 mandibular cartilage acquires a greater length, and 

 the suspensorium becomes reduced in proportion and 

 shifted backwards. 



