i9o:i. 



AXATOMY OF THE .TAPANKSE SALAMAXDEU. 



305 



no fenestrse — at least visible fenesti'se. This flap appears to be 

 purely membranous. Anteriorly it is continuous with the rest 

 of the interauricular septum, which, on the contrary, is entirely 

 mviscular. It is much fenestrated, and consists below of vertical 

 pillars passing from the dorsal to the ventral wall of the auricle. 

 There is also, paiticulai-ly on the side adjoining the fibrous part 

 of the septum, a mesh-like disposition of the muscular strands 

 such as Huxley has figured in Menobranchus *. The completeness 

 of the separation of two auricles, not indicated externally, I may 

 i-epeat, is furthermore shown by the fact that they debouch 

 quite independently of each other into the ventricle. The septum 

 between the two auricles is almost suggestive of a heart- valve in 

 being partly muscular and partly membranous. And it may 

 possibly be the case that the septum is physiologically something 

 more than a mere partition-wall — and incomplete at that — be- 

 tween two neighbouring cavities. It may possibly by its own 



Text-fig. 30. 



Auricular septum oi Mefialohatrachus, viewed from in front. 

 1'he membranous part is clotted. 



contraction, by the contiuctions of the muscular part playing 

 upon the tendinous sheet, do something to stop or facilitate at 

 different periods of the heart's beat the admixture of arterial 

 and venous blood before it reaches the ventricle. I greatly regret 

 that, having only one large heart at my disposal, I am unable to 

 push this matter any further. 



I do not find myself absolutely in accord with the account of 

 the interaui'icular septum given by Hyrtl or with his figure of the 

 same. Hyi-tl desciibes the septum as extremely delicate but 

 imperforate, and as arching over the atrio-ventricular orifice. It 

 is clear that this is only that part of the septum which I have 

 described as thin and imperforate. Hyrtl does not refer to the 

 muscular pillars which tie down the rest of the thin, and in parts 



Proc. Zool. See. 



* Loc. cit. pi. 32. fig. 5. 



-1903, Vol II. No. XX. 



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