. On the anatomy of vertebrates [electronic resource] . r valve; butthese are the only i columneecarneae in the right ventricle;there being none of a pyramidal form projecting into the cavity,nor any chordae tendineae. The principal valve which guardsthe auricular aperture is a strong muscular fold, figs. 90, 91,92, /, nearly as thick as the wall of the ventricle itself, extend-ing from the fleshy column above mentioned obliquely clown-ward and backward to the angle formed between the septumand the free wall of the ventricle at the lower and posteriorpart of the cavity. The convex edge of this
. On the anatomy of vertebrates [electronic resource] . r valve; butthese are the only i columneecarneae in the right ventricle;there being none of a pyramidal form projecting into the cavity,nor any chordae tendineae. The principal valve which guardsthe auricular aperture is a strong muscular fold, figs. 90, 91,92, /, nearly as thick as the wall of the ventricle itself, extend-ing from the fleshy column above mentioned obliquely clown-ward and backward to the angle formed between the septumand the free wall of the ventricle at the lower and posteriorpart of the cavity. The convex edge of this muscular valveis turned toward the convex projection made by the septum,and must be forcibly applied to this part during the systole ofthe ventricles; so that, while all reflux into the auricle is pre-vented, additional impulse is given to the flow of blood throughthe pulmonary artery ; the muscular parietes of the ventriclebeing thus complete at every part except at the orifice of theartery. This valve is strongest in the Diving Birds, weakest in 91. Ventricles of the heart of a Swan. 188 ANATOMY OF VERTEBRATES. the St ruth ions, and especially in the Apteryx, in which it is par-tially membranous and has its margin tied by a few tendons to afleshy process from the fixed ventricular wall. The small muscular column, fig. 92, m, at the upper part ofthe auricular orifice is analogous in its position to the single valvewhich guards the corresponding orifice in Reptiles; the Cro-codiles alone present a second muscular valve (vol. i. p. 510, , r) homologous with the larger valve in Birds. The right ventricle is remarkable for the smoothness and even- ness of its inner surface. Thepulmonary artery is provided atits origin with three semilunarvalves, fig. 92, n. It divides, asusual, into two branches, fig. 168,one for each lung; the rightbranch passes under the arch ofthe aorta. The aerated blood is returnedfrom the lungs by two veinswhich open into the back part ofthe left aur
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