VI.] 



THE COMMON FROG. 



79 



like manner, and in the tadpole accordingly we find 

 an apparatus similar to that of the Siren. There are, 

 in fact, on each side of the throat, four branchial 

 arches, placed behind another arch, which is con- 

 nected with the skull. As development proceeds 

 these branchial arches become gradually absorbed 

 and all but disappear. Relics of them, however, 

 exist even in the adult condition, and thus serve to 

 indicate the true nature of parts which otherwise 

 would be little understood. 



The central portion of the structure — that from 

 which arches diverge on each side — increases in 

 relative as well as absolute size, and becomes the 



Fig. 43.— Diagram of the changes undergone by the hyoid in a Frog in passing from 

 the Tadpole stage to the adult condition (constructed from Parker's Memoir). 

 Uppermost left-hand figure, the youngest condition ; lowest right-hand figure, the 

 adult, h, the hyoidean arch, ultimately the corniculum ; b'^—bA, the four branchial 

 arches which become gradually atrophied, the cornua (or thyro-hyal) th being 

 their representative in the adult ; b' , another branchial rudiment ; bk, the body of 

 the hyoid. 



" body " of the os hyoidcs. That arch on each side 

 which is connected with the skull and is placed im- 



