IX.J 



THE COMMON FROG. 



1S7 



This venous blood is sent out from the heart 

 through a bulbous aorta, whence arise on each side 

 a series of arteries which ascend the branchial arches, 

 one on the outer side of each such arch, decreasing in 

 size as it ascends. (Fig. 8i.) 



Fig. So. — Two lamellse (or leaflets) from the gills of an Osseous Fish, showing the 

 course of the respiratory circulation, s, cut surface of one of the branchial arches. 

 On its upper side is seen a concavity which is produced by the section of the 

 groove which runs along the conve.x and exterior (here upper) side of each bran- 

 chial arch, ba, branchial arterj' in section, giving off the gill arteries (,ga) to the 

 adjacent sides of the gill leaflets, whence the blood is distributed in the leaflets ; 

 gv, the gill veins which run along the outer side of the gill leaflets, collecting the 

 blood from them by minute veins and pouring it into bv, the branchial vein, 

 which runs up the groove of the branchial arch and has the branchial artery 

 superficial and exterior to it. 



Each branchial artery gives off small gill arteries, 

 which run along one edge of each little membranous 

 leaflet or gill, and supply it with minute branches 

 ending in capillaries, in which the blood is purified. 

 There the purified blood is taken up by minute veins 

 which open into gill veins, one of which runs along 

 the opposite edge of each gill to that occupied by the 

 gill artery. 



