890 



ANGIOLOGT. 



valve or valve of Thehesius, is a fold of the endocardium which 

 covers the coronary sinus, preventing regurgitation of blood 

 during the contraction of the auricle. The foramina Thebesii 

 are minute openings on the inner surface of the auricle ; some of 

 them are mere depressions, whilst others are the openings of 

 minute veins, vencB cordis minimce, which return blood directly 

 from the substance of the walls. The right auriculo-ventricular 

 opening is a large oval aperture, occupying the floor of the 

 auricle ; it communicates with the right ventricle. The tuber- 

 culum Lowerii is a slight projection situated between the 

 openings of the cavse, and is supposed to direct the blood from 



the anterior cava into the 

 auriculo-ventricular open- 

 ing. 



In man the remains of a 

 foetal structure, called the 

 Eustachian valve are situ- 

 ated at the anterior margin 

 of the posterior cava, stretch- 

 ing from it to the left side 

 of the annulus ovalis. It 

 is a doubling of the lining 

 membrane, largest in the 

 foetus, and serves to direct 

 the blood from the vein to 

 the foramen ovale; in quad- 

 rupeds, this structure, if 

 present at all, is extremely 

 rudimentary. 



The fossa ovalis is an 

 oval depression in the interauricular septum, being an obliter- 

 ated foramep, which in the foetus joins the right and left 

 auricles. At birth this opening is closed. Its lower border 

 is indistinct ; its upper thick and projecting, forming the 

 annulus ovalis or isthmus Vieusseni. The musculi pecti- 

 nati are columns of muscular fibres situated chiefly in the 

 appendix; they are called pectinati, from their resemblance in 

 arrangement to the teeth of a comb. Smaller bundles cross 

 the large ones, giving the whole a reticulated appearamce, 

 between which are depressions, some of which are the foramina 

 Thebesii 



Fio. 150. 

 Right side of the heart— laid open. 1, Eight ven- 

 tricle ; a a, Its external wall ; b b, Carneae columnse ; 

 c, Great moderator band ; d, Origin of pulmonary 

 artery ; e e e, Sigmoid valves ; 2, Eight auricle ; a a, 

 Foramina Thebesii and mijsculi pectinati ; b, Opening 

 •of anterior, and c, of posterior vena cava. 



