The Heart. 



377 



Aorta ascendens 



Auricula dextra 



('onus arteriosus 



Arteria iiulnionali 



Vena cava superior 



Atrium sinistrum - 



Foramen ovale 



Valvula 

 foraminis ovalis 



Vena cava inferior 



Ventriculns dexter 



I Ostium veuosum ventriculi dextri 



Valvula venae cavae [inferioris, Eustachii] Valvula sinus coronarii [Thebesii] 



423. Right fore -chamber (atrium dextnim) of a foetal 



heart iS"' month), viewed from the right. 



(A part of the wall of ihf^ atrium lias been removed. Magnification: 2:1.) 



From the upper wall of the atrium dextriim projects the bluntly wedge-shaped auri- 

 cula dextra (right auricle of the heart) (0. T. right auricular appendix). It curves around 

 the first portion of the aorta ascendens to the left, is notched above and below but otherwise 

 smooth; it presents inside numerous irregular erossmg muscular columns, trabecnlae curneue. 



During foetal life the two atria commimicate with one another through an opening, the 

 foramen ovule situated at the spot which later is the fossa ovalis. At its margin in front 

 and al)Ove it is surrounded b_v a horseshoe-shaped, powerful band of muscle, which later becomes 

 the limbus fossae ovalis, and behind and below it is bounded by the concave margin of the 

 valvula foraminis ovalis, which rises as a thin connective tissue plate from behind and below 

 and projects, gToove-like, uito the left atrium. Just after birth, as soon as the pressure in 

 the left atrium becomes higher than in the right, this valve is pressed upon the lunbus and fuses 

 with it almost completely, often, however, leaving a small slit open. The valvida foraminis 

 ovalis becomes accordingly later the floor of the fossa ovalis; the anterior concave margin of 

 the valve is often retained and is visible inside the left atrium on the septal surface. 



The yeutriculus dexter (right ventricle) (see Figs. 411 415, 417420 and 424) 

 has the shape of a wedge ; its left concave surface is attached to the right side of the left 

 ventricle: its apex does not reach the apex of the heart. The base of the wedge is hidden 

 by the attacbment of the right atrium ; the inferior, the right and the superior anterior surfaces 

 lie free ; the latter goes veiy gradiuilly over into the arteria pulmonalis and, in the distended 

 heart, projects markedly convexly forward (conus arteriosus). On the inside, marking off the 

 conus arteriosus from the venous portion of the ventricle, is a muscidar projection (crista 

 supraventricularis) which extends, arch-like, from the base over the septum toward the apex 

 and then to the right to the superior anterior wall and becomes lost in the roots of the large 

 papillary m\iscle. The venous portion presents at the septum a fairly smooth wall, but else- 

 where very many trabecidae carneae (see p. .371). The ostium venosum can be closed by the 

 valvula tricuspidalis (tricuspid valve) ; this presents (see Fig. 419) a large cusp adjoining 

 the interventricular septum (cuspis medialis), further a small cuspis anterior corresponding 

 about to the conus arteriosus, a large cuspis posterior turned toward tlie right fi'ee wall, and, 

 usually, between the cuspis medialis and cuspis posterior an additional small intermediary cusp. 



