MODIFICATIONS OF THE AORTIC ARCHES. 



83 



fourth pair and the subvcrtebral 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. 



Mn. JTy. BrJ J3r.^ Bn^ Bn^Br^ Br:° Bi:'' 



I I ' 1 L i I I 





TAT). 



-AC 



n m IV" V VI \ui viu K 



Fig. 25. — A diagram intended to show the manner in which the aortic arches become modi- 

 fied in the series of the Verteh?xtta. 



k. A hj-pothetically perfect series of aortic arches, correspondinf^ with the nine postoral vis- 

 ceral arches, of which evidence is to be found in some Sharks and M/rrslpobrmichii. 

 AG. Cardiac aorta; AB. Dorsal or sub vertebral aorta, i-ix the aortic arches corre- 

 sponding with 3/«., the mandibular; Hy., the hyoidean, and Br. ' — Br.'., the seven 

 branchial viscci-al ai-ches. i, ii, in, iv, v, vi, vii, the seven branchi<il clefts. The lirst 



