1058 



VERTEBRATED ANIMALS 



resembling those of fishes, are seen the rudiments of the internal 

 gills, which soon bagin to be developed in the stead of the preceding. 



FIG. 792. Circulation in the tadpole. 



1. Anterior portion of young tadpole, showing the external gills, with the incipient 

 tufts of the internal gills, and the pair of minute tubes between the heart and the 

 spirally coiled intestine, which are the rudiments of the future lungs. 

 . -.- 2. More advanced tadpole, in which the external gills have almost disappeared : 

 a, remnant of external gills on the left side ; 6, operculum ; c, remnant of external gill 

 on the right side, turned in. 



8. Advanced tadpole, showing the course of the general circulation : a, heart ; 

 I branchial arteries ; c, pericardium ; d, internal gill ; e, first or cephalic trunk ; 

 /,' branch to lip ; f/, branches to head ; h, second or branchial trunk; i, third trunk, 

 uniting with its fellow to form the abdominal aorta, which is continued as the caudal 

 artery" k, to the extremity of . the tail; I, caudal vein; m, kidney; n, vena cava ; 

 o liver ; p, vena portse ; q, sinus venosus, receiving the jugular vein, r, and the ab- 

 dominal veins, f, u, as also the branchial vein, v. 



4 The branchial circulation 011 a larger scale : A, B, C, three primary branches of 

 the branchial artery ; a., cartilaginous arches ; b, additional framework ; c, e, twigs of 

 branchial artery ; d, f, rootlets of branchial vein. 



5. Origin of the vessels of the internal gills, #, from the roots of those of the 

 external. 



6. The heart, systemic arteries, pulmonary arteries and veins, and lungs, in the 

 adult frog, the heart being turned up in the right-hand figure, to show the junction 

 of the pulmonary veins and their entrance into the left auricle. 



