644 ARTERIES OF PISCES. 



side of the throat (figs. 363, abr, and 364, a), which, with a few 

 exceptions to be noticed below, divides into as many branches on 

 each side as there are visceral arches. These branches, after 

 traversing the visceral arches, unite on the dorsal side of the 

 throat into a common trunk on each side. This trunk (figs. 363 

 and 364) after giving off one (or more) vessels to the head (c and 

 c] turns backwards, and bends in towards the middle line, close 

 to its fellow, immediately below the notochord (figs. 21 and 116) 

 and runs backwards in this situation towards the end of the tail. 

 The two parallel trunks below the notochord fuse very early into 

 a single trunk, the dorsal aorta (figs. 363, ad, and 364, a"}. 



FIG. 363. DIAGRAMMATIC VIEW OF THE HEAD OF AN EMBRYO TELEOSTEAN, 

 WITH THE PRIMITIVE VASCULAR TRUNKS. (From Gegenbaur.) 



a. auricle; v. ventricle; abr. branchial artery; c'. carotid; ad. dorsal aorta; 

 ^. branchial clefts; j. sinus venosus; dc. ductus Cuvieri; n. nasal pit. 



There is given off from each collecting trunk from the visceral 

 arches, or from the commencement of the dorsal aorta, a subclavian 

 artery to each of the anterior limbs ; from near the anterior end 

 of the dorsal aorta a vitelline artery (or before the dorsal aortse 

 have united a pair of arteries fig. 125, R of A and L of A) to the 

 yolk-sack, which subsequently becomes the main visceral artery 1 ; 

 and from the dorsal aorta opposite the hind limbs one (or two) 

 arteries on each side the iliac arteries to the hind limbs ; from 

 these arteries the allantoic arteries are given off in the higher 

 types, which remain as the hypogastric arteries after the 

 disappearance of the allantois. 



The primitive arrangement of the arterial trunks is with a 

 few modifications retained in Fishes. With the development of 

 the gills the vessels to the arches become divided into two parts 

 connected by a capillary system in the gill folds, viz. into the 



1 In Mammalia the superior mesenteric artery arises from the vitelline artery, 

 which may probably be regarded as a primitive CEeliaco-mesentevic artery. 



