178 THE CIRCULATORY APPARATUS 



and the auriculoventricular orifice. It is semilunar 

 in form, the free concave margin sending one cornu 

 to join the front of the annulus ovalis and the other to 

 the auricular wall. The fossa ovalis, at the back of the 

 septum, in the situation of the fetal foramen ovale, 

 its prominent margin being known as the annulus 

 ovalis. The musculi pectinati, small elevated columns 

 which traverse the appendix and the adjacent part 

 of the sinus. 



The Right Ventricle. This is pyramidal, and extends 

 nearly to the apex of the heart. It is bounded inter- 

 nally by the convex surface of the wall of the ven- 

 tricles, and prolonged above and internally into a 

 pouch, the infundibulum, or conus arteriosus, from 

 which springs the pulmonary artery. Its cavity has 

 a capacity of three ounces. On opening the ventricle 

 the following parts are presented for examination: 



The auriculoventricular orifice, oval in form, and 

 placed near the right side of the heart. Around its 

 circumference is a fibrous ring, and it is guarded by 

 the tricuspid valve. The opening of the pulmonary 

 artery, circular in form, at the summit of the conus 

 arteriosus, near the septum; is guarded by the pul- 

 monary valves (semilunar) . The tricuspid valve consists 

 of three triangular flaps formed of fibrous tissue covered 

 by endocardium. They are continuous with one 

 another at their bases, and their free margins and 

 ventricular surfaces give attachment to the chordae 

 tendinese. Their central part is thick and strong, the 

 lateral margins thinner and flexible. The chorda 

 tendinece are attached as follows: several to the attached 

 margin of each flap, blending with the fibrous ring; 

 several to the strong central part; and the finest and 

 most numerous to the margins of each curtain. The 

 columncB carneoe are projecting bundles of muscular 

 substance found all over the ventricular wall excepting 

 the conus arteriosus. They afford attachment for 

 the papillary muscles. The three semilunar valves 



