VI 



AETEMAL SYSTEM 



395 



disHXT tiVel { Sm S the a .° rtic arGh Can be traced throughout as a 

 ell, t i ^ m th . e Am ™ta, where the walls of the gill- 



r ^.B. 



dJc. «c. c,r. z. 



Fig. 186. — Scheme of aortic arches and their derivatives as seen from the ventral side. 

 The parts of the original scheme which disappear during, development are shown in 

 pale tone. 



A, complete unmodified series of aortic arches ; B, irrangement in a. Urodele ; C, in a Reptile ; 

 D, in a Mammal. A, dorsal aorta; a.r, aortic root; a. anastomotic vessel; e.e, common carotid; 

 d.B, duct of Botallus ; d.c, dorsal (internal) carotid ; %, in minate artery ; l.p, left pulmonary artery ; 

 l.s, left systemic ; p, pulmonary ; r.p, right pulmon ry ; , ".systemic aorta ; j, subclavian artery ; 

 v.a, ventral aorta ; v.c, ventral (external) carotid ; I, I , etc., aortic arches. 



The longitudinal vessels with which the aortic arches are con- 

 nected are prolonged forwards as the carotid arteries which supply 

 the head with blood. The ventral aorta is prolonged forwards as the 

 ventral, or external, carotid while the prolongation forwards of the 

 aortic root forms the dorsal, or internal, carotid. Of the alternative 



