THE HEART. 187 



Its office in the foetus is clearly, according to the opinion of Sa- 

 batier, to direct the blood of the ascending cava through the fo- 

 ramen ovale. In the adult, it may, on the general principle of 

 venous valves, oppose itself to the introduction of refluent blood 

 into the ascending cava; but this office cannot be very impor- 

 tant, as the valve is frequently scarcely visible at that age. 



At the lower part of the right auricle, just to the left of the 

 Eustachian valve and very near it, is the orifice of the large co- 

 ronary vein of the heart: it is protected by a small semi-lunar 

 valve, (Valvula T/iebesii,) formed also by a duplication of the 

 lining membrane of the auricle. This orifice will admit a quill 

 of common size very readily. 



Between the right auricle and ventricle is a round hole, of 

 more than an inch in diameter, for the, passage of the blood ; it 

 is the Ostium Venosum. Its margin, on the auricular side, is 

 smooth and rounded. 



The parietes of the right auricle are formed by muscular 

 fibres. On the sinus these fibres are collected into small trans- 

 verse fasciculi, called Musculi Pectinati, from their resembling 

 the teeth of a comb. These fasciculi, though slightly united 

 by other fibres, yet leave between them deep interstices, by 

 which the external and the internal membrane of the heart come 

 into contact. The parietes of the auricle are about one line in 

 thickness. Its muscular structure is continued for a short dis- 

 tance, on the two vena3 cavas. There are several orifices of 

 small veins on the internal surface of this cavity, and in greater 

 abundance around the fossa ovalis; they belong to the system 

 of coronary vessels, and are the foramina Thebesii. 



The right Ventricle (Ventriculus Dexter, anterior.) The 

 general form of this cavity, which receives the blood from the 

 right auricle, is that of a triangular pyramid, curved somewhat 

 backwards, and having its base downwards*. It forms the great- 

 er part of the anterior surface of the heart, and is about three 

 lines in thickness. It is bounded on its posterior face by the 

 left ventricle, from which it is completely separated by a thick 

 septum. 



The internal surface of this cavity is covered by muscular 

 fasciculi, of very irregular shapes and dimensions, designated 

 under the term of Columnar Carneae : some of the latter go from 



