284 



CLASS AMPHIBIA. 



, 12 



pulmo-cutaneum. The position of these is reversed at the ventricular 

 opening (where the valve is attached ventrally), the cavum pulnio- 

 cutaneum being on the right and the cavum aorticum on the left. Inas- 

 much as the longitudinal valve runs to the right valve on the right side 

 of the ventricular opening, it is clear that the cavum pulmo-cutaneum, 

 which at this point is, as above described, on the right side of the conus, 

 does not lead into the ventricular opening but is cut off from it by the 

 longitudinal valve (Fig. 158). The cavum aorticum on the other hand 

 leads behind right into the ventricle. The result of this arrangement is 

 that when the conus becomes functionally divided into two chambers, 

 as it does when it contracts, and the free edge of the longitudinal valve 

 meets the opposite wall, the cavum pulmo-cutaneum is completely cut off 



from the ventricle and ends blindly. 

 Anteriorly the longitudinal valve 

 is connected (Fig. 159) -with valve 

 No. 1 (the valve on the right side 

 of the anterior end of the conus), 

 which is very large and extends 

 right across the conus, so that the 

 middle point of its free edge is at- 

 tached to the opposite wall (left) 

 of the conus between the other two 

 valves (2 and 3) (Fig. 160, A, a). 

 Turning now to the ventral aorta, 

 wo find that the horizontal sep- 

 tum, which in Salamandra divides it 

 anteriorly into a ventral portion con- 

 tinupus with the carotid and aortic 

 arches, and a dorsal portion con- 

 tinued into the pulmonary arches 

 (Fig. 157), here reaches back to the 

 hind end of the ventral aorta (Fig. 

 159), and is attached posteriorly to 

 the inner (concave) surface of the 

 valve No. 1 (trs, Fig. 100). The 

 left hand side of the hind end of 

 this septum is attached to the 

 valve at the point where the latter 

 is fused with the left hand 

 wall of the conus between valves 



2 and 3^ (Fig. 160, A, a). The result of this arrangement is that the 

 ventral aorta is completely divided into two passages of which the dorsal 

 (pr.lmonnry) opens behind into the cavum pulmo-cutaneum of the conus 

 (left), the opening being guarded by valve No. 2 and one half (16, dorsal) 

 of the divided valve No. 1, while the ventral passage (carotid and aortic) 

 leads into the cavum aorticum with valve No. 3 and the other half (1 a) 

 of valve No. 1. It is further to be noted, and this is a highly interesting 

 point, that the two carotid arches open by a common opening into the 

 right aortic arch (Fig. 159), thus foreshadowing the arrangement found 

 in Reptiles. 



The object of these elaborate arrangements in the conus and ventral 

 aorta of tho higher Amphibia is to ensure a proper distribution of the 

 pulmonary and venous blood along the outgoing arteries. Tn the Urodeles 



"17 



FlG. 158. Heart of Rana opened by a longi- 

 tudinal horizontal section, ventra'l view of 

 the dorsal half (after Gaupp). 1 right 

 auricle ; 2 dorsal, 5 right of the three 

 proximal valves of the conus ; 3 longi- 

 tudinal valve of the conus ; 4 conus arterio- 

 sus ; 8 see above ; 6 right auriculo-ventri- 

 cular valve ; 7 spongy part of ventricle ; 



8 clear central space of ventricle ; 



9 dorsal auriculo- ventricular valve ; 10 

 interauricular septum; It left auricle; 

 12 ostium venae pulmonalis ; 13 ostium 

 sinus venosi. 



