224 



PHYSIOLOGY. 



numerous projecting ridges in the right ventricle which are muscles 

 called the columnar carneae. Some of them are named, from their 

 shape, the papillary muscles, which project from the interior surface 

 of the ventricle and end in narrow tendinous cords called the chordae 

 tendineae. 



The right auriculo-ventricular orifice opens into the ventricle 

 at its lower back part. From its edges projects a broad, membran- 

 ous fold divided into three parts and hence called the tricuspid, 

 whose free borders are attached by the chordae tendineae to the 



Fig. 64. Diagram of Mammalian Heart. (BECLAED.) 



a, Left ventricle. 6, Right ventricle, c, Left auricle, d, Right auricle. 

 /, Aorta, g, g, Pulmonary arteries. Ji, Inferior vena cava. i, Superior vena 

 cava. fc, Orifice of superior vena cava. I, Orifice of inferior vena cava. tn, 

 Orifice of the coronary vein, o, Left pulmonary vein, p, Right pulmonary vein. 

 r, Orifice of the right pulmonary vein. , Orifice of the left pulmonary vein. 



papillary muscles and to other .points on the interior surface of the 

 ventricle. When the valve is open the three parts lie against the 

 interior surface of the ventricle. The duplicature of the endo- 

 cardium with included fibrous tissue makes up the tricuspid valve 

 and the chordae tendineae. The pulmonary artery springs from the 

 base of the right ventricle. Its opening is provided with three 

 semilunar valves. These valves are three crescentric doublings of 

 the endocardium with fibrous tissue and are arranged in a circle. 

 Their convex border is attached around the edge of the orifice of 



