174 CIRCULATORY SYSTEM. 



is lined by a fine, vascular membrane, and presents internally a 

 polished surface, the regularity of which is interrupted in places 

 by many fleshy prominences, named the musculi pectinati ; be- 

 tween which are numerous little sinuses, or cul-de-sacs, that, as 

 well as the fleshy pillars themselves, vary much in size, and are 

 most numerous and remarkable within the appendix, or ear-like 

 portion of the auricle, where they form together a reticulated 

 structure. Three venous trunks terminate in this cavity : the 

 vena cava anterior opens into the superior and posterior part of it ; 

 the vena cava posterior opens into the inferior and posterior part ; 

 and the coronary vein just below it. The vena azygos forms a 

 junction with the anterior cava just as the latter pierces the auri- 

 cular parietes. Between the openings made by the two venae 

 cavse, there is a prominence that is usually called the tubercalum 

 Loweri. There is a deep sac or sinus at the entrance of the pos- 

 terior cava ; and between this and the mouth of the coronary 

 vein, a crescentic valvular Jiap, which projects half way over the 

 mouth of the latter vessel. The right auricle has a free commu- 

 nication with the right ventricle by an aperture of large size, 

 called the auriculo-ventricular opening. 



One auricle is divided from the other by a muscular partition, 

 denominated the septum auricular um ; in which may be seen, 

 when the part is held to the light, an elliptical inlet of semi- 

 transparent membrane, crossed in places by fleshy fasciculi, which 

 takes the name of fossa ovalis : in some subjects there is a small 

 aperture through it, and this is all that remains of the foramen 

 ovale. 



The right ventricle is redder and considerably thicker in 

 substance than the right auricle: like it, it commonly contains, 

 after death, a large coagulum of blood. It is likewise lined by a 

 smooth, polished membrane, and has within it numerous^es//j/ 

 pillars, which, instead of being reticulated as those are in the 

 auricle, are disposed longitudinally. In addition to these, there 

 are three conspicuous fleshy prominences, from their size named 

 the carntfE columncB, from which several little tendinous cords, 

 chorda ttndinea,, proceed to the edoes of three membranous and 

 fibrous productions (sometimes distinguished by the name of cor- 

 tina tendinea) that close the auriculo-ventricular opening : the ap- 

 paratus altogether forms the valvula tricuspis. Other cords, similar 

 to the cord'cB tendinea, but stronger than them, pass between the 

 outer wall and the septum. The pulmonary artery emerges from 

 the upper and back part of this cavity ; and its mouth is guarded 

 by three semilunar valves, which present little pouches within the 

 cavity of the vessel : these valves consist of doublings of the lining 

 membrane of these parts, infolding, about the middle of their loose 



