'////; HI-ART. :.n:, 



tendinous cords; 4, An internal face, which becomes superior when the 

 valve is raised to close the opening, at which period it constitutes the floor 

 of the auricular cavity. 



Piilnii'iinrii ojii'iiinif. This orifice represents the embouchure of the 

 pulmonary artery. Situated in front and to the left of the preceding, and 

 a little higher, it occupies the summit of a kind of infundibulum formed by 

 the left compartment of the ventricle being prolonged upwards. It is 

 perfectly circular, smaller than the artery to which it gives origin, as well 

 as the auriculo -ventricular opening, from which it is separated by a species 

 of muscular sptir, to which is 



attached the principal festoon Fig. 261. 



of the tricuspid valve. 



The pulmonary opening is 

 furnished with three valves : the 

 xi'jiitn'nl (or semicircular), sus- 

 pended over the entrance to the 

 pulmonary artery, and, as has 



M ingeniously remarked (by 

 Winslow), like three pigeon's 

 nests joined in a triangle. 

 These valves arc remarkable for 

 their thinness ; a circumstance 

 which docs not interfere with 

 their solidity. They present : 

 an external, convex border, at- 

 tached to the margin of the 

 orifice and to the walls of the 

 pulmonary artery; a free bor- 

 der, straight when pulled tense, 

 concave when left to itself, and 

 sometimes provided in its middle 

 with a small, though very hard, 

 the nockue f Antnium 

 Ai-nittii > : a superior, 

 concave face; and an inferior, convex one. The sigmoid valves arc raised 

 and applied to the walls of the vessel whose entrance they garnish, wlnn 

 the ventricle contracts and sends the venous blood into the lung. When 

 contraction ceases, they fall back one against the other by that part 

 of their inferior face next to their free border, so as to oppose the reflux of 

 tin- Mood into the ventricular cavity. 1 ' 



Kii;iiT AIKICM-:. The cavity of the right auricle represents a very 



concave lid or cover surmounting the auriculo-vcntrieiilar opening, and 



is prolonged, anteriorly, by a curved <;//-<// -xac. It offers for study this 



Vor cul-de-sac, a posterior, external, and //- nut I trull, us well as a superior 



SECTION OF THE HEART AT THE LEVEL OF TI1K 

 VALVES. 



P, Pulmonary artery ; A, Aorta ; M, Mitral valve ; 

 T, Tricuspid valve. 



1 It 1ms been repeated, ad nauseam, that the occlusion of the, nrtfiinl 

 from tli<- juxtaposition of tin' // />;</ / of the Mmnoid valves; even tin- Mimll tu 

 in tin- middle of thin bonier has IM-CII con.-idcrcd t<> play its pint in rlnMii tin- triangular 

 1 .-pace left when these, vnlvi-s HIM t. In P:I.MUI,' the linger into tin- pulmonary 

 artery of a living miinml, to explore the function of then- nicinbrnniis f-'ld., it b n adily 

 . v d li .it !!: y c mi' in contact by a lurre |>oitioii of tlieir convex fai-e. :ui.l n.'t ;ili>m- 

 by tlu ir Iret; b.nder. Thin amusement is stidi, th.it \\e have with niiu-li ililtienlty trii .1 

 \> produce ;r.i iiihiillicii ney uf contact by K'-pin:; one of the \ahrs up :i-;iin.-t tin- 

 walls of tin PCM I \\.lh the finder; but the others came di\\U ii::.iin.- 1 tH linger and 

 applial tin m.elveti uroiind it H> as to i \nctly clo0 tlic Orifice. 



