306 



COMPARATIVE ANATOMY 



muscular conus arteriosus (Fig. 246, A) : these are most numerous 

 in Elasmobranchs and Ganoids. There is a tendency, however, for 

 the posterior valves, or those which lie nearest the ventricle, 



D.C.s 



FIG. 245. HEART OF A, Zygcma malleus, FROM THE VENTRAL SIDE ; B, OF Acan- 

 thias vulyaris, FROM THE DORSAL SIDE, WITH THE ATRIUM CUT OPEN (after 

 Rose) ; C, OF A TELEOST (Silurus glanis). 



A, A, atria ; a, a, auricular appendages ; F, ventricle ; tr (in B) and Ba (in C), 



bulbus arteriosus ; tr (in A) and co (in B), conus arteriosus, tr (in C), ventral 



aorta. 

 D.C.d and D.C.s, right and left precavals ; V.a.d. and V.a.s, right and left 



valve of the sinus venosus ; O.a.v, atrio- ventricular aperture ; l,a 4,a, 



afferent branchial arteries. 



gradually to undergo reduction (B). The most anterior row always 

 persists, and corresponds to the single row of valves between the 

 ventricle and bulbus in Teleosts (c) and Cyclostomes. Together 

 with the reduction of these valves, the conus arteriosus also be- 

 comes reduced in the last-mentioned forms, so that the non- 



