166 THE ANATOMY OF VERTEBRATED ANIMALS. 



aorta. The anterior branchiag are replaced by tlie carotid 

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

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

 brancliice 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 

 3oiled up into a close spire, like a watcli-sjDring, 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 TIrodela the tail persists, and develops complete 

 vertebrae ; but, in the JBatrachia, 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. 



