CHAP. XXVIII.] PERICARDIUM AND ENDOCARDIUM. 335 



of the right auricle, passing downwards and forwards ; the inferior 

 cava opens into its lower angle, passing upwards, backwards, arid 

 inwards. The coronary vein opens between the mouth of the in- 

 ferior cava and the auriculo- ventricular orifice. 



On laying open the right auricle, by an incision extending 

 between the two venae cavse, an intricate arrangement of muscular 

 bundles called musculi pectinati, may be seen on its outer wall. 

 These fleshy columns interlace freely with each other. On the 

 septum a depression exists about its middle, called the fossa ovalis, 

 nearly surrounded by a thick fleshy ring called the annulus ovalis. 

 This marks the situation of the orifice already alluded to, which 

 existed during intra-uterine life the foramen ovale. 



To the left of the orifice of the inferior vena cava there is a 

 valvular process, which is another remnant of a mechanism adapted 

 to the circulation through the heart in intra-uterine life. This is 

 the Eustachian valve. It is a process of the inner membrane of the 

 auricle, of semilunar shape, which projects between the vena cava 

 and the auriculo-ventricular orifice, and in the foetus served to 

 direct the ascending current of blood through the foramen ovale 

 into the left auricle. The orifice of the coronary vein is guarded 

 by a small valve called the valve of Thebesius. Several small 

 orifices are seen scattered over the inner surface of the right 

 auricle, called foramina Thebesii-, some of these are the openings of 

 small veins from the wall of the auricle ; others merely lead into 

 depressions between the muscular fibres of the auricular wall. 



Four veins pour their blood into the left auricle ; these are the 

 right and left pulmonary veins, two on each side. The left veins 

 open quite close to each other. The left auricle is placed in the 

 concavity of the aorta, and has, lying in front of it, the roots of both 

 the aorta and the pulmonary artery. 



The inner surface of the left auricle is perfectly smooth, covered 

 with an opaque lining membrane, which appears somewhat thicker 

 than that of the right side. There is no appearance of musculi 

 pectinati in the left sinus venosus ; a few, however, exist on the 

 inner wall of the auricular appendage. Here and there some 

 orifices are seen leading to depressions in the wall of the sinus 

 venosus. On the left side of the septum between the auricles we 

 observe traces of the valve-like portions of the septum which formed 

 the immediate boundary of the foramen ovale during foetal life. 



Of the Pericardium and Endocardium. The heart is enclosed in 

 a fibrous bag, the fibrous pericardium, which is closely adherent 

 below to the central tendon of the diaphragm, and above becomes 



