MODIFICATIONS OF THE AORTIC ARCHES. 



83 



fourth pair and the subvertebral aorta. The dorsal ends of 

 the first, second, and third arches become obliterated ; but 

 their cardiac ends, and the branches which they give off, be- 

 come the arteries of the head and upper extremities. 



Mh. mi. J}/-.' En' Bn^ Bn'Bn' Bn" Br.' 



I I I I I I I I L 



Ch. 



iimililililC 



f^e, "js, — A diagram Intended to show the manner in which the aortic arches becomft modi- 

 fied in the series of tiie Vertebrata. 



k. A hypottietically perfect series of aortic arches, corresponding with the nine postoral vis- 

 ceral arches, of which evidence is to be found in some Shai-ks and Mm's-ipobranchii. 

 AC. Cardiac aorta; AI). Dorsal or subvertebral aorta, i-ix the aortic arches corre- 

 Bpondlng- with JiJi., the mandibular; Hy,^ the hyoidean, and Br.^ — ^j?r. '^, the seven 

 branchial vlscoral arches, i, ii, m, rv, v, vi, ni, the seven itranchial clefts. The firs! 



