REPORT ON THE SPHENISCID^. 139 



of the valve is, moreover, prolonged transversely across the wall of the auricle, and comes 

 into relation with the orifice of the left superior cava, which it in part defends. The 

 valvular apparatus at the mouth of the left superior cava, however, is much less eflfective 

 than that met with in connection with the other two caval orifices. The fossa ovalis is 

 well marked. Beneath the raised margin which surrounds it, a small cul-de-sac extends 

 forwards from the auricular cavity. There is no aperture of communication between 

 the right and left auricles, but doubtless the presence of the cul-de-sac in question is 

 due to the closure of the originally open foramen ovale. 



The cavity of the right ventricle (PI. XL fig. 2) resembles in form that of other birds. 

 The wall which is formed by the septum ventriculorum is almost smooth and devoid 

 of muscular bands, while the opposite or anterior wall is rough, owing to the presence 

 of numerous decussating muscular bundles. The right auriculo-ventricular valve is 

 arranged as in the majority of birds, but the two muscular fiaps which form it are relatively 

 stronger than in most. The left or smaller flap, which in some birds, e.g. the Emeu, is 

 so small as to be scarcely distinguishable, is in the Penguins of large size, although of 

 course smaller than the right flap, which in all birds is the larger of the two. The 

 orifice of the pulmonary artery is provided with three semi-lunar valves. 



The cavity of the left auricle (PI. XI. fig. 3) receives the pulmonary veins — one from 

 each lung. Thej^ open on the upper wall of the left auricle. These orifices are usually 

 described as being destitute of any valves, but in the Penguins I find a muscular structure, 

 which may, and I believe does, act as an incomplete valve to these orifices. This structure 

 consists of a shelf-like muscular fold, which extends across the upper wall of the auricle 

 from side to side, being attached to the auricular wall in front of the two openings of the 

 pulmonary veins, over which it hangs like a curtain. It aj^pears to me that when the 

 auricle contracts this curtain must be thrown across the orifices of the pulmonary veins, 

 and thus prevent the regurgitation of blood from the auricular cavity into these vessels. 

 The lower wall of the left auricle presents a few muscular bundles, but the upper wall is 

 uniformly smooth. 



The wall of the left ventricle (PI. XL fig. 3) is nearly twice as thick as that of the 

 i-ight. It is provided with numerous columnse earner, which have a very regular 

 arrangement, and decussating with one another at regidar intervals form the boundaries 

 of small diamond-shaped spaces on the ventricular wall. The columnee carnese are met 

 with on every portion of the wall of this ventricle. In section this ventricle is circular, 

 while the right is semi-lunar in form. The left auriculo-ventricular valve consists of two 

 cusps, which are disposed much as in the mammalian heart. The chordse tendineee 

 attached to them spring in some species from the wall of the heart, in others from 

 rudimental papillary muscles. The latter, when present, are, so far as I have observed, 

 always three in number. Two are placed opposite the intervals between the two cusps 

 composing the valve, to both of which they supply chordae tendinese, while the thii'd 



