HEART. 117 



tinuous with the inner coat of the vessels. When it passes 

 from an auricle to a ventricle, or from a ventricle to an 

 artery, it forms duplicatures, or valves, in which fibrous 

 tissue is inclosed. 



The Eustachian valve is situated between the lower cava 

 and the auriculo-ventricular opening; it is a semilunar fold, 

 sometimes rudimentary and sometimes developed into a 

 well-formed valve with a reticulated margin. During foetal 

 life this structure serves to direct the blood from the inferior 

 cava toward the foramen ovale. 



The coronary valve is occasionally connected with the 

 preceding ; this also is a semilunar fold stretching across 

 the orifice of the coronary sinus, which enters the auricle 

 just below the inferior vena cava. 



The foramina Thebesii are the apertures of minute veins 

 found in various parts of the cavity, and which, coming 

 from the muscular structure of the heart, pour their con- 

 tents directly into the auricle. 



The fossa ovalis is a rounded depression situated on the 

 septum between the auricles, characterized by a well-defined 

 margin, and called the annulus ovalis; it is the remains of 

 the foramen ovale of fnetal life. Not'unfrequently the annu- 

 lus forms a sort of valve upon one side of the fossa, beneath 

 which a probe may be insinuated and passed into the left 

 auricle, the foramen remaining imperfectly closed; this may 

 be consistent with an undisturbed condition of the circu- 

 lation. 



The musculi pectinati are parallel muscular columns, 

 symmetrically arranged, and chiefly confined to the parietes 

 of the auricular appendix. 



The auriculo-ventricular orifice consists of a fibrous ring, 

 with which are connected the folds of membrane consti- 

 tuting the tricuspid valve. 



The right ventricle is opened by introducing one blade of the scissors 

 through the auriculo-ventricular orifice, and incising its wall along the 

 outer edge, nearly to the apex of the heart ; from the ventricle pass 

 the scissors into the pulmonary artery, and make an incision, which, 

 commencing at the termination of the former, shall pass upward, par- 

 allel to the ventricular septum, dividing the pulmonary artery. The 

 V-shaped flap thus made, when lifted, will expose the ventricle. 



The RIGHT VENTRICLE is remarkable for its fleshy bands 

 and the generally irregular character of the surface of its 

 cavity ; near the aperture of the pulmonary artery, how- 

 ever, its walls become comparatively smooth. 



