THE DOGFISH 



36i 



an organ of doubtful function (p. 51) which does not belong 

 to the vascular system, lies below the anterior end of the 

 ventral aorta as a pear-shaped body with the stalk forwards. 

 From the afferent branchial arteries the blood passes into the 

 capillaries of the gills, where it is oxygenated and gathered 

 up into efferent branchial arteries. These form a complete 

 loop round each of the first four clefts, the loops being 

 joined fore and aft by short horizontal vessels at about the 

 middle of their lengths. The last cleft, having no gill on 

 its hinder side, has an efferent vessel on its front side only, 

 and all the blood of this vessel passes by the horizontal 



Q.mM. eoel, a. 



FIG. 259. — A diagram of the arterial system of a dogfish, 

 seen from the right side. 



a.b.a., Afferent branchial arteries ; a.mes., anterior mesenteric artery ; c.c, common 

 carotid artery; cd., caudal artery; coel.a., cceliac artery; d.ao., dorsal aorta; 

 e.b.a., efferent branchial arteries ; e.c, external carotid artery ; epibr., epibran- 

 chial arteries; hi., heart; hep., hepatic artery; ky.a., hyoidean artery (this 

 joins the internal carotid of the opposite side, which is not shown); i.e., 

 internal carotid artery; il.a., iliac artery; lH.g., lienogastric artery; ov., 

 ovarian artery; p.c, posterior carotid artery; p.mes., posterior mesenteric 

 artery ; ren., renal arteries ; scl.ft., subclavian artery ; v.ao., ventral aorta. 



vessel into that of the gill in front. From the dorsal end 

 of each of the complete loops arises a vessel known as an 

 epibranchial artery, which runs backwards and inwards on 

 the roof of the pharynx to join the median dorsal aorta 

 opposite to its fellow of the other side. From the dorsal 

 end of the first efferent branchial artery, just outside the 

 origin of the first epibranchial artery, arises the common 

 carotid artery. This runs forwards and inwards under the 

 skull. Behind the orbit it divides into an external and 

 an internal branch. The former immediately passes through 

 the opening we have mentioned (p. 347) and runs forwards 

 along the floor of the orbit to supply the upper jaw and the 



