580 



HEART. 



posterior and inferior. The entrance of the 

 superior cava looks downwards and forwards 

 in the direction of the body of the auricle ; the 

 entrance of the cava inferior is directed up- 

 wards, backwards, and inwards. These two 

 orifices are circular, and that of the cava infe- 

 rior is larger than that of the cava superior. 

 The right margins of these veins are continuous 

 with each other ; the left or anterior margins 

 are continuous with the auricle, which in fact 

 appears at first sight to be formed by an ex- 

 pansion of the veins ; hence the term sinus 

 venosus. Around the left margin of the en- 

 trance of the cava superior there is a prominent 

 band of muscular fibres; and around its right 

 and posterior margin there is another but less 

 prominent band placed at its angle of junction 

 with the right margin of the inferior cava. This 

 last band occupies the position of the sup- 

 posed tubercle of Lower (tuberculum Loweri). 

 The cava inferior occasionally forms a dilata- 

 tion immediately before it enters into the au- 

 ricle. The venae cavae have properly no valves 

 at their entrance into the auricles.* The fossa 

 ovalis ( valvula foraminis ovalis, vestigium Jb- 

 ra minis ovalis), which marks the position of 

 the foramen ovale by which the two auricles 

 communicated freely with each other in the 

 fetus, is seen at the lower and right portion of 

 the auricle, partly placed in a notch in the 

 posterior and lower part of the fleshy portion 

 of the septum, and partly in the upper part of 

 the vena cava ascendens as it passes in to form 

 the sinus venosus. The upper and anterior 

 margins of this depression are thick and pro- 

 jecting (annulus sen isthmus Vieusseni, columns 

 Jbraminis ovalis). This was supposed by Vi- 

 eussens to prevent the blood of the cava supe- 

 rior from falling into the cava inferior, an effect 

 which Lower also imagined might be produced 

 by the tubercle which he supposed was placed 

 at the junction of the two veins. We have 

 already pointed out that the orifices of the two 

 veins are placed in different directions, which 

 is sufficient to prevent the descending column 

 of blood falling directly upon the ascending. 

 The posterior and lower margins of the fossa 

 ovalis are ill-defined. The surface of the de- 

 pression is sometimes smooth, at other times 

 uneven and reticulated. Betwepn the upper 

 margin of the depression and the annulus or 

 thickened edge of the fossa ovalis we frequently 

 find a small slit passing from below upwards, 

 and forming a valvular opening between the 

 two auricles. The remains of the Eustachian 

 valve (foraminis ovalis anterior valvula) may 

 be seen running from the anterior and left side 

 of the entrance of the cava inferior to the left 

 side of the fossa ovalis, where it attaches itself 

 to the annulus. This valve exhibits very va- 

 rious appearances in the adult: sometimes it is 

 very indistinctly marked, at other times it is 

 sufficiently apparent, and much more rarely it 

 approaches the size which it presents in fetal 

 life. It is frequently reticulated. Its convex 



* The Fustachian valve cannot be considered as 

 essentially connected with the cava inferior in the 

 adult. 



margin is attached to the surface of the vein 

 and auricle ; its concave margin is free ; its su- 

 perior and convex surface looks towards the 

 auricle, and its lower and concave surface to- 

 wards the entrance of the vein. Placed to the 

 left of the Eustachian valve, and between it 

 and the upper and outer part of the base of the 

 ventricle, is the orifice of the coronary vein. A 

 valve (valvula Thebesii), the free and concave 

 margin of which is directed upwards, covers 

 the entrance of this vein. It is sometimes im- 

 perfect, occasionally reticulated. Instead of 

 one coronary valve we may have two or more, 

 one placed behind another. These two valves, 

 viz. the Eustachian and Thebesian, are formed 

 by a reduplicature of the lining serous mem- 

 brane of the heart. 



The Eustachian valve frequently, however, 

 contains some muscular fibres at its fixed mar- 

 gin. A number of small openings (foramina 

 Thebesii) may be seen on the inner surface of 

 the auricle, some of which lead into depres- 

 sions ; others are the orifices of small veins. 

 The muscular fibres projecting from the ante- 

 rior and outer surface, already alluded to, pass 

 vertically from the auricle to the edges of the 

 auriculo-ventricular opening. These, from their 

 supposed resemblance to the teeth of a comb, 

 are termed musculi pectinati. Smaller bun- 

 dles cross among the larger, giving the inner 

 surface at this part a reticulated appearance. 

 At the places where the transverse fibres are 

 deficient, the outer and inner serous mem- 

 branes of the heart lie in close contact. In the 

 floor or base of the auricle there is a large oval 

 opening leading into the ventricle (right au- 

 riculo-ventricular opening), having its upper 

 margin surrounded by a white ring. The up- 

 per part of this ring has a yellowish colour 

 from the auricular tendinous ring being here 

 translucent, so that the fat lying in the auri- 

 cular groove is seen through it. 



Right ventricle (ventriculus anterior, v. dex- 

 ter,v.pulmonalis.) External surf ace. The right 

 ventricle occupies the anterior and inferior por- 

 tion of the right side of the heart. Its form is 

 pyramidal, the base looking towards the au- 

 ricle, its apex towards the apex of the heart. 

 Its walls are much thicker than those of the 

 auricle. This thickness arises from the in- 

 creased number of its muscular fibres. 



Internal surface. The right ventricle may 

 be best opened by making an incision along its 

 right edge from the base to the apex, and 

 another from the root of the pulmonary artery 

 along its anterior surface near the septum to 

 join the other at the apex. On examining the 

 interior, its internal and posterior walls are 

 seen to be common to it and the opposite 

 ventricle, the anterior and external walls to 

 belong exclusively to itself. Its posterior and 

 internal walls are convex, its anterior and 

 internal concave. Its posterior and external 

 walls are decidedly shorter than its internal and 

 anterior. Its parietes are rather thinner at their 

 attachment to the anterior margin of the septum 

 than along its posterior margin. They are also 

 considerably thinner at the apex than towards 

 the base. * A number of fleshy columns 



