976 



A MANUAL OF ANATOMY 



is a crescentic fold of endocardium, which is the remains of the 

 Eustachian valve of foetal life. The convexity of the crescent is 

 continuous with the anterior margin of the orifice of the vein, and 

 the inner horn of the crescent is continuous with the anterior limb 

 of the annulus ovalis, to be presently described. The fold is a 

 somewhat indefinite structure in the adult, being subject to much 

 variety as regards size, and sometimes presenting several small 

 openings. During foetal life, however, the Eustachian valve is 

 of the utmost importance, inasmuch as it directs the blood entering 

 by the inferior vena cava through the foramen ovale into the left 

 auricle. 



The orifice of the coronary sinus is situated between the vestigial 

 Eustachian valve and the auriculo-ventricular orifice. It is 



Arch of Aorta 



Superior Vena Cava 



Right Pulmonary^' 

 Veins ^^ 



Pulmonary Artery 



Right Auricle ._ 



Pulmonary Orifice — 



Inferior Vena Cava 



Left Pulmonary 

 Veins 



Left Auricle 



- — Aortic Orifice 



.Interventricular Septum 



Fig. 399. — Diagrammatic View of the Interior of the Heart (after 



Milne Edwards). 



guarded by a delicate semicircular fold of the endocardium, called 

 the coronary valve, or valve of Thebesius, which, however, is function- 

 ally incompetent. 



The foramina Thebesii represent several minute openings on 

 the wall of the atrium. Some of these are simply blind recesses, 

 whilst others are the orifices of minute veins, called the vencr 

 minimcB cordis, which return the blood from the wall of the auricle. 



The auriculo-ventricular, or tricuspid, orifice is situated in the 

 lower and anterior ]xart of the atrium, in front of the orifice of the 

 inferior vena cava, with the intervention oi that of the coronary 

 sinus. It is oval, and, in health, the index, middle, and ring fingers, 



