THE HEART. 



589 



ventricular opening, from which it is separated by a kind of muscular spur, to 

 which is attached the principal festoon of the tricuspid valve. 



The pulmonary opening is furnished with three valves — the sigmoid (or semi- 

 lunar), snspeiid.'d over the entrance to the pulmonary artery, and, as has been 

 ingeniously remarked (by Winslow), like three pigeons' nests joined in a triangle. 

 These valves are remarkable for their thinness — a circumstance which does not 

 interfere with their solidity. They present : an external, convex border, attached 

 to the margin of the orifice and to the walls of the pulmonary artery ; a free 

 border, straight wlien pulled tense, concave when left to itself, and sometimes 

 provided in its middle with a small, very hard tubercle, the nodule of Arantius 

 (nodal us, or corpus Arantii) ; a superior, concave face ; and an inferior, convex 

 one. The sigmoid valves are raised 

 and applied to the walls of the vessel 

 at its entrance, when the ventricle 

 contracts and sends the venous blood 

 into the lung. Wlien this 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 the blood into 

 the ventricular cavity.^ 



Right Auricle. — The cavity of 

 the right auricle represents a very 

 concave lid or cover surmounting the 

 auriculo-ventricular opening, and is 

 prolonged, anteriorly, by a curved 

 cul-de-sac. It offers for study this 

 anterior cul-de-sac, dt. posterior, external, 

 and interned ivcdl, as well as a superior 

 wall or roof, and the auriculo-ventri- 

 cular opening, which occupies the 

 whole floor of the cavity. This ori- 

 fice has been already described. 



The (Ulterior cul-de-sac is in the appendix auricularis ; it is divided by a great 

 number of muscular columns of the second and third orders {musculipectin(tti), 

 into deep and complex areoke. 



The posterior ivcdl responds to the interauricular septum ; it is smooth, and 

 usually marked by an oblique and more or less deep cul-de-sac (or depression), 

 the remains of Botal's foramen. This depression is surrounded by the ring (or 

 isthmus) of Vieussens {annulus ovcdis), and is named the fossa oralis ; it is only 

 separated from the left auricular cavity by a thin membrane, a vestige of the 



SECTION OF THE HEART AT THE LEVFL OF THE 

 VALVES. 



p, Pulmonary artery; A, aorta; ii, mitral valve; 

 T, tricuspid valve. 



' It ha8 been repeated, ad naugeam, that the occlusion of the arterial openings results from 

 the juxtaposition of the free border of tlie sigmoid valves; even the small tubercle in the 

 middle of this bonier, has been considered to play its fiarl in closino; the triani^idar central 

 space left when these valves meet. In passing the finger into the pulmonary artery of a livicg 

 animal, to explore Ihe function of these membranous folds, it is readily perceived tiiat they 

 come in contact by a large portion of their convex face, and not alone by their free border. 

 This arrangement is such, that we have with much diflSculty tried to produce an insufficiency 

 of contact by keeping one of the valves up against the walls of th£ vessel with the finger; but 

 the others came down against the finger and applied themselves around it so as to exactly close 

 the orifice. 



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