THE VASCULAR SYSTEM 



lects the blood from the 

 arches and conveys it to 

 all parts of the body, the 

 ventral and dorsal aortse 

 respectively (Fig. 91, a), f 

 In all the diagrams the 

 parts of both sides are 

 shown, viewed ventrally 

 and flattened out so that 

 the ventral aorta lies in 

 the middle and the dorsal 

 aortse converge from the 

 outer sides. In selach- 

 ians (Fig. 91, b) five of 

 these arches are present 

 and functional; each arch 

 is divided into an afferent 

 and an efferent branch, 

 between which respiration 

 is effected by means of 

 capillaries spread out over 

 soft endodermic gills. 

 From the anterior portion 

 of the efferent system the 

 carotids are given off, 

 vessels which include the 

 only remnants of the first 

 arterial arches. 

 /fin the urodelous am- 

 phibians (Fig. 91, c) the 

 first two arterial arches 

 disappear in the embryo, 

 leaving four functional 

 arches. Of these arch 

 III unites with remnants 

 of I and II to form the 

 carotids, IV and V on 



FIG. 91. Diagrams showing modifi- 

 cations in the arterial arches of Ver- 

 tebrates. 



(a) Typical, embryonic, (b) Fishes. (c) 

 Amphibians. (d) Reptiles. (e) Birds. (f) 

 Mammals. 



/, //. ///, IV, V, VI, arterial arches; of, 

 Art. carotis dextra; cs. Art. carotis sinistra; 

 sd, Art. subclavia dextra; ss, Art. subclavia 

 sinistra; ad, Aorta dextra; ay, Aorta sinistra; 

 bd. Ductus Botalli dexter; bs, Ductus Botalli 

 sinister; pd, Art. pulmonalis dextra; ps t 

 Art. pulmonalis sinistra. 



