DEVELOrEJIENT OF BATRACIIIA. 



G27' 



Newt I^Triton). CCLXXXII. 



f gills ; larval 



a size that gives it the character of the aortic arch. The pul- 

 monary vessel, 4, now 

 equals in size the trunk, 

 3, of which it was a 

 branch ; and it exceeds 

 the tributary 21. 



With the total disap- 

 pearance of the gills the 

 blood of the foremost 

 vascular arch is carried 

 into the two chief ar- 

 teries of the head, fig. 

 437,12,1s; either directly, 

 or by the transformation 

 of the anastomotic channel into a recurrent origin of one of these : 

 it is thus converted into the carotid arteries. In higher Eeptilcs 

 the origins of 1, 1, are blended or produced into a common trunk 

 of the carotids. 



The next vascular arch, 2, 2, is now transformed into the right 

 and left arch of the aorta, by the enlargement of the anastomotic 

 channel u, fig. 435; with changes in length and position by which 

 it gives off the cutaneous artery of the neck, 15. The tributary, 21, 

 to the pulmonary artery, 4-19, is now shortened, and transverse in 

 position : in higher Reptiles it is still more shortened, and finally 

 obliterated as the ' ductus arteriosus ' on each side. The orljital 

 arterjr, is, fig. 436, and 11, fig. 437, continues to be sent off from 

 the aortic arch. 



The first or hindmost of the primitive vascular arches is now 

 converted into the pulmonary artery, 

 and the blood which was transmitted 

 by 3, figs. 435 and 436, is now diverted 

 from the largest of the gills to the 

 lungs. 



The blastema, which lays the foun- 

 dation of the lungs, is situated behind 

 and at the sides of the fore part of 

 the alimentary canal, where it enters 

 the bucco-branchial cavity. The 

 lunf^s begin to be formed as soon as 

 the intestine behind has taken on its 

 first sigmoid curvature. They are 

 not developed from the alimentary 

 canal, but communicate with it soon 



437 



Changes in In ancbi.il vessels after aljsorp 



tion of KllK: Newt. CCLXX7T. 



after the establishment 



