442 SCHULTE, SET WHALE. 



position of the intervenous tubercle (Loweri). Entally the atrio-ventricular rings are very 

 prominent and from them many muscular trabeculse radiate to the walls of the auricles, which 

 by their caudal margins overhang and conceal the atrio-ventricular sulcus. This holds true 

 only of the ventral and lateral margins of the venous ostia; mesad and dorsad the rings sink 

 to the level of the respective walls of the heart. The right auricle has a crista terminalis con- 

 forming in extent to the sulcus of the same name ectally. From this trabeculse extend in an 

 irregular manner to the wall of the auricle. On the left side there was an arched ridge from 

 beside the upper pulmonary vein, bifurcating laterally and being attached to the atrio-ventri- 

 cular ring at two points. From this also trabeculse were given off. On neither side had the 

 musculature of the auricle anything approaching a pectinate arrangement. 



The right atrium is noteworthy for the total suppression of the right sinus valve. As in 

 other Cetacea there is no Eustachian and no Thebesian valve. The large orifice of the coronary 

 sinus has however a sharp and slightly overhanging margin in the caudal half of its contour. 

 The limbus fossae ovalis is a well defined but narrow frame to the fossa, which is placed immedi- 

 ately caudad of the intervenous tubercle. The atrial septum as has been said is small and the 

 atria diverge widely ventrad, as in reptiles, and for the same cause, the great size of the vessels 

 to be accommodated between them. The valve of the fossa ovalis is highly peculiar in that it 

 is attached in its entire circumference to the limbus and has no free edge. It protrudes in the 

 left atrium as a long funnel or cornucopia with a fenestrated fundus. Knox l described it in 

 the heart of a foetal Balcena mysticetus as "a membranous sac, the size of a full-sized thimble, 

 presenting at the bottom a delicate reticulated network, and projecting into the left auricle." 

 Turner 2 from whom this quotation is borrowed describes the structure in a foetus of B. musculus 

 measuring 19 ft. 6 in. in length. "In the interauricular septum an almost circular foramen 

 readily admitting five extended digits was situated. Surrounding this opening and attached 

 to its edge, a loose, membranous, annular fold, formed by a duplication of the endocardium was 

 seen. When put on the stretch it projected into the auricle, and the projecting border was free 

 and pierced with large fenestrse. Although this fold was situated in the right auricle, when I 

 opened into that cavity, yet it could without difficulty be passed through the foramen into the 

 left auricle. At the attached border, again, the membrane was almost entire, and most perfect in 

 its anterior, external and posterior portions, where the depth from the attached to the free margin 

 was four inches." In this foetus the valve measures 7 mm. in length. The foramen at the limbus 

 6 mm. by 4 mm. The funnel depended completely free into the left atrium and was not main- 

 tained in position by reticnacula, save that near its base ventrally a very small fold, like a minute 

 frenulum, connects it with the wall of the atrium. In a much larger heart from a foetal Megaptera 

 preserved in spirits by Mr. Andrews, the valve had the same general character, but had con- 

 tracted adhesions ventrally with the atrial wall for about one third its length. These were not 

 sufficient to prevent the valve from being inverted into the right auricle, where it was found folded 

 and collapsed as in Turner's specimen. In the adhesions at the base of the valve may be seen 

 the initiation of a process of closure, which appears to differ from that known in other vertebrates. 

 Were these adhesions to continue distad to the fundus of the valve, its ventral portion would 

 become fused with the atrial wall in its whole extent. The remainder would then occupy a posi- 



1 Knox, R. Catalogue of Anatomical Preparations of the Whale. Edinburgh, 1838. 



- Turner, Wm. An Account of the great finner whale stranded at Longniddy (Balcenoplera Sibaldii). Trans. Roy. Soc. Edin., 



1872. 



