CH. XVIII.] THE HEART. 2O/ 



Right Ventricle. The right ventricle occupies the chief part of 

 the anterior surface of the heart, as well as a small part of the 

 posterior surface ; it forms the right margin of the heart. It 

 takes no part in the formation of the apex. On section its cavity, 

 in consequence of the encroachment upon it of the septum ventri- 

 culorum, is semilunar or crescentic (fig. 210); into it are two 

 openings, the auriculo-ventricular at the base and the opening 

 of the pulmonary artery also at the base, but more to the left ; 

 both orifices are guarded by valves, the former called tricuspid 

 and the latter semilunar. In this ventricle are also the pro- 

 jections of the muscular tissue called columnce carnece (described 

 at length p. 210). 



Left Auricle. The left auricle is situated at the left and posterior 

 part of the base of the heart, and is best seen from behind. It is 

 quadrilateral, and receives on either side two pulmonary veins. 



Cavity of right ventricle. -B B C^ty of left ventricle. 



Fig. 210. Transverse section of bullock's heart in a state of cadaveric rigidity. (Ualton., 



The auricular appendix is the only part of the auricle seen from 

 the front, and corresponds with that on the right side, but is 

 thicker, and the interior is smoother. The left auricle is only 

 slightly thicker than the right. The left auriculo-ventricular 

 orifice is oval, and a little smaller than that on the right side. 

 There is a depression on the septum between the auricles, which is 

 a vestige of the foramen between them, that exists in fo3tal life. 



Left Ventricle. Though taking part to a comparatively slight 

 extent in the anterior surface, the left ventricle occupies the 

 chief part of the posterior surface. In it are two openings very 

 close together, viz. the auriculo-ventricular and the aortic, guarded 

 by the valves corresponding to those of the right side of the heart, 

 viz. the bicuspid or mitral and the semilunar. The first opening 

 is at the left and back part of the base of the ventricle, and the 

 aortic in front and towards the right. In this ventricle, as in the 

 right, are the columnre carnese, -which are smaller but more 

 closely reticulated. They are chiefly found near the apex and 



