178 



THE FKOG. 



length of the efferent vessel ; while very nearly the whole length 

 of the afferent vessel, and all the gill capillaries, disappear 

 completely. 



Very slight changes will now convert the branchial system 

 of the tadpole to the aortic system of the adult frog. Of the 

 four aortic arches, the first, in the first branchial arch, becomes 

 the carotid arch of the frog (Fig. 81, i). The portion of the 

 dorsal aorta between the points of opening of the first and 

 second aortic arches remains an open tubular vessel for some 

 time, and may even retain its lumen in the adult. More usually, 

 however, the cavity becomes obliterated, and the walls of the 



FIG. 81. Diagrammatic figure of the arterial system of an adult male 



Frog, from the right side, x 1. 



a, stomach, b, nostril, c, small intestine, ca, carotid artery, cf, carotid eland . 

 cm , coehaco-mesenteric artery, en, cutaneous artery. <l. large 'intestine, da, dorsal 

 lorta. /, lemur, fl, spleen. //, hepatic artery. , right lung, la, lingual arterv. m, 

 Wtt. o, kidney, oa, occipito-vertebral artery, pa, pulmonary artery, r, pelvic: 

 girdle, s, sternum, sa, subclavian arterv. sc, sciatic arterv. t, tongue, ta, trnncus 

 arteriosus. ua, urinogenital arteries, v, ventricle. 1, carotid arch. 2, svstemic arch. 

 3, puluio-cutaneous arch. 



vessel persist merely as a pigmented band, connecting the dorsal 

 ends of the carotid and systemic arches with each other. After 

 the obliteration of this part of the aorta, the blood in the carotid 

 arch is distributed exclusively to the head. 



The second aortic arch, in the second branchial arch of the 

 tadpole, becomes the systemic arch of the frog (Fig. 81,2). 



The third aortic arch, in the third branchial arch of the tad- 

 pole, disappears altogether. In young frogs of the first year it 

 loses its connection with the aorta, and then gradually shortens 

 up, the distal part becoming a solid cellular cord, and the 

 proximal or cardiac part retaining for a time its lumen. Before 

 the end of the first year this vessel has entirely disappeared. 



