THE HEART 561 



musculi pectinati. These end behind in a vertical smooth ridge, the crista termi- 

 nalis (Fig. 418). 



The Right Ventricle (ventriculus dexter} is pyramidal in form, and extends from 

 the right auricle to near the apex of the heart. Its antero-supenor surface is rounded 

 and convex, and forms the larger part of the front of the heart. Its under surface 

 is flattened, rests upon the Diaphragm, and forms a small part of the postero- 

 inferior surface of the heart. Its posterior wall is formed by the septum between 

 the two ventricles, the interventricular septum (septum vejitriculorum), which bulges 

 into the right ventricle, so that a transverse section of the cavity presents a semilunar 

 outline. The basal and inner angle of the ventricle is prolonged into a conical 

 pouch, the infundibulum (conus arteriosus), from which the pulmonary artery 

 arises. The balance of the ventricle, the body, is the portion into which the auriculo- 

 ventricular orifice opens. The conus arteriosus is marked off from the body of 

 the ventricle by a muscular projection (crista supraventricidaris). The walls 

 of the right ventricle are thinner than those of the left, the proportion between 

 them being as 1 to 3. The wall is thickest at the base, and gradually becomes 

 thinner toward the apex. 



To examine the interior of the right ventricle, its anterior wall should be turned downward 

 and to the right in the form of a triangular flap. This is accomplished by making two incisions: 

 (1) From the pulmonary artery to the apex of the ventricle parallel to, but a little to the right 

 of, the anterior interventricular furrow; (2) another, starting from the upper extremity, of the 

 first and carried outward parallel to, but a little below, the auriculoventricular furrow, care 

 being taken not to injure the auriculoventricular valve. 



The interior of the right ventricle presents for examination: 



Q | Auriculoventricular. 



1 Opening of the pulmonary artery. 



( hemilunar. 

 Columnae carneae. Chordae tendineae. 



The right auriculoventricular opening, or the tricuspid orifice (ostium venosum 

 ventriculi dextri), is the large oval aperture of communication between the auricle 

 and ventricle. It is situated at the base of the ventricle, near the right border of 

 the heart. The plane of this opening is nearly vertical. It is oval and about 

 3.75 cm. (1.5 inches) in diameter from side to side, surrounded by a fibrous ring 

 and covered by the lining membrane of the heart; it is considerably larger than 

 the corresponding aperture on the left side, being sufficient to admit the ends of 

 four fingers. The circumference of the orifice is about 12 cm. (4.8' inches) in 

 the male, and 10.5 cm. (4.2 inches) in the female. It is guarded by the tricuspid 

 valve. 



The opening of the pulmonary artery (ostium arteriosum pulmonis) is circular in 

 form, and is situated at the summit of the conus arteriosus, close to the ventricular 

 septum. It is placed above and to the left of the auriculoventricular opening, and 

 is guarded by the pulmonary valve. 



The tricuspid valve (valvula tricuspidalis) consists of three segments or cusps 

 (cuspides) of a triangular or trapezoidal shape, each formed by a duplicature of 

 the lining membrane of the heart, strengthened by intervening layers of fibrous 

 tissue. The largest and most movable segment is placed toward the left side of 

 the auriculoventricular opening, and is interposed between that opening and the 

 infundibulum; hence it is called the left or infundibular cusp (cuspis medialis). 

 Another segment is in relation with the right part of the front of the ventricle, the 

 right or marginal cusp (cuspis anterior), and a third with its posterior wall, the 

 posterior or septal cusp (cuspis posterior). The central part of each segment is 



36 



