RIGHT AURICLE. 507 



Near this fossa is a large semilunar plait, or valve, with its 

 points and concave edge uppermost, and convex edge down- 

 wards. It was described by Eustachius, and therefore, is 

 called the Valve of Eustachius. 



It commences at the lower surface of the opening of the 

 inferior vena cava, and runs forwards to terminate below the 

 fossa ovalis. It served in the foetus to obstruct the passage 

 of the venous blood from the right auricle into the right ven- 

 tricle, and to direct it in a great measure through the foramen 

 ovale. 



Anterior to this valve, and near the union of the auricle and 

 ventricle, is the orifice of the proper vein of the heart, or the 

 coronary vein. This orifice is covered by another semilunar 

 valve, which is sometimes reticulated.* 



The aperture, which forms the communication between the 

 right auricle and right ventricle, is about an inch in diameter, 

 and is called ostium venosum. From its whole margin arises 

 a valvular ring, or duplicature of the membrane lining the 

 surface : this circular valve is divided into three angular por- 

 tions, which are called Valvula Tricuspides. From their 

 margins proceed a great number of fine tendinous threads, 

 which are connected to a number of distinct portions of mus- 

 cular substance, which arise from the ventricle. 



The Right Ventricle, when examined separately from the 

 other parts of the heart, is rather triangular in its figure, It is 

 composed entirely of muscular fibres closely compacted ; and 

 is much thicker than the auricle, although not so thick as the 

 other ventricle. Its internal surface is composed of bundles or 

 columns of fleshy fibres, which are of various thickness and 

 length. Some of these columns (columna carne<z) arise from 

 the ventricle, and are connected with the tendinous threads, 

 (chorda tendinea?) which are attached to the margin of the 

 tricuspid valves : the direction of them is from the apex of the 



* The orifice is called the foramen Thebesii, and the valve valvula Thebesii, 

 from the anatomist who first described them. 



There are several other orifices in the neighborhood of the foramen of The- 

 besius, by which some of the lesser coronary veins discharge into the right 

 auricle. p. 



