DISSECTING MANUAL. 



foetal foramen ovale; this is bounded above and in front by 

 a raised margin (annulus ovalis). A thin endocardial fold 

 (Eustachian valve) stretches from the front of the annulus 

 ovalis to the anterior and lower edge of the inferior vena cava 

 orifice; just below this is another fold (Thebesian valve) over 

 the coronary sinus. In the antero-inferior boundary is the 

 opening (tricuspid orifice) into the right ventricle. Scattered 

 over the walls are small fossae (foramina Thebesii) into which 

 the venae minimi cordis often open. [787] 



Interior of Left Auricle. This is smooth and only has mus- 

 culi pectinati in the appendix. The pulmonary veins enter the 

 upper part of the posterior surface; foramina Thebesii are 

 scattered about. In the antero-inferior boundary is an oval 

 aperture (mitral orifice) leading to the left ventricle. [788] 



Ventricles. This part is conical and flattened. A central 

 fibre-cartilage lies in the triangle between the aortic and 

 auriculo- ventricular orifices, and is continuous with the fibrous 

 rings surrounding the latter. Endocardium lines the cavities. 

 The interventricular septum is oblique, the right side looking 

 somewhat forward ; it is chiefly muscular, but the upper and 

 posterior part (pars membranacea) is fibrous and thin oppo- 

 site the aortic vestibule. The walls of the left ventricle, except 

 the septum, are three times as thick as those of the right ven- 

 tricle. [788] 



Interior of Right Ventricle. The cavity is triangular and 

 divisible into anterior (infundibulum, or conns arteriosus) 

 and posterior (body) parts, separated by a muscular fold; the 

 infundibulum has smooth walls. The body has, on its walls, 

 numerous muscular bundles (columnae carneae) of three sorts ; 

 the simplest are mere ridges; others are rounded bundles, free 

 in the middle but attached at each end, one of them (moder- 

 ator band) running from the septum to the base of the anterior 

 papillary muscle. The third kind (musculi papillares) are 

 conical bundles attached to the wall at their bases but ending 

 at their apices in fine tendinous cords (chordae tendinea?) . Of 



[126] 



