534 



ANGIOLOGY 





The musculi pectinati, fewer and smaller than in the right auricula, are confined 

 to the inner surface of the auricula. 



On the atrial septum may be seen a lunated impression, bounded below by a 

 crescentic ridge, the concavity of which is turned upward. The depression is 

 just above the fossa ovalis of the right atrium. 



Left Ventricle (ventriculus sinister). The left ventricle is longer and more conical 

 in shape than the right, and on transverse section its concavity presents an oval 

 or nearly circular outline. It forms a small part of the sternocostal surface and a 

 considerable part of the diaphragmatic surface of the heart; it also forms the apex 

 of the heart. Its walls are about three times as thick as those of the right ventricle. 



Its interior (Fig. 496) presents the following parts for examination: 



^ . 

 Openings 



Trabeculse carnea?. 



Left atrio ventricular. 



A7 , (Bicuspid or Mitral. 

 Valves JAortic 

 Chorda? tendinese. 





The left atrioventricular opening (mitral orifice) is placed below and to the left 

 of the aortic orifice. It is a little smaller than the corresponding aperture of the 

 opposite side, admitting only two fingers. It is surrounded by a dense fibrous ring, 

 covered by the lining membrane of the heart, and is guarded by the bicuspid or 

 mitral valve. 



Aortic sinus 



Nodulus 

 Lunula 



Left post, 

 valve 



Origins of coronary arteries 



Right post, valve 



Ant. valve 



Fia. 497. Aorta laid open to show the ser 



ir valves. 



The aortic opening is a circular aperture, in front and to the right of the atrio- 

 ventricular, from which it is separated by the anterior cusp of the bicuspid valve. 

 Its orifice is guarded by the aortic semilunar valves. The portion of the ventricle 

 immediately below the aortic orifice is termed the aortic vestibule, and possesses 

 fibrous instead of muscular walls. 



The bicuspid or mitral valve (valvula bicuspidalis [metralis]) (Figs. 495, 496) is 

 attached to the circumference of the left atrioventricular orifice in the same way 

 that the tricuspid valve is on the opposite side. It consists of two triangular cusps, 

 formed by duplicatures of the lining membrane, strengthened by fibrous tissue, 

 and containing a few muscular fibers. The cusps are of unequal size, and are larger, 

 thicker, and stronger than those of the tricuspid valve. The larger cusp is placed 

 in front and to the right between the atrioventricular and aortic orifices, and is 

 known as the anterior or aortic cusp ; the smaller or posterior cusp is placed behind 

 and to the left of the opening. Two smaller cusps are usually found at the angles 

 of junction of the larger. The cusps of the bicuspid valve are furnished with chordae 

 tendinea?, which are attached in a manner similar to those on the right side; they 

 are, however, thicker, stronger, and less numerous. 



