166 THE ANATOMY OF VERTEBRATED ANIMALS. 



aorta. The anterior branchiee are replaced by the carotid 

 glands, and their afferent vessel is the carotid passage of the 

 adult. The afferent and efferent trunks of the third pair of 

 branchiae are converted into the stem of the cutaneous artery, 

 and the afferent trunk of the fourth pair of branchiae into that 

 of the pulmonary artery. The diagram (Fig. 25, p. 83) is 

 intended to make these changes, and the relations of the 

 various trunks to the embryonic aortic arches, intelligible. 



The alimentary canal of the Tadpole is, at first, long, and 

 soiled up into a close spire, like a watch-spring, in the ab- 

 domen, but its length becomes relatively less as age advances. 

 At the same time, the diet changes from vegetable to animal 

 — the young tadpole being chiefly herbivorous, the adult, 

 insectivorous. 



In the TTrodela the tail persists, and develops complete 

 vertebrae ; but, in the Satrcichia, the caudal part of the spinal 

 column disappears, for the most part, together with the rest 

 of the tail, and only the basal portion of the notochord be- 

 comes converted into the urostyle, which eventually anchyloses 

 with the two hindermost neural arches. 



