AORTIC VALVE. 



251 



tliicker and stronger in all its parts, and consists of only two pointed 

 segments, continuons at their attached bases. The larger of the two 

 segments is suspended obliquely to the right and in fi'ont of the other, 

 Ijetween the aniicnlar and aortic openings : the smaller to the left and 

 posteriorly, and close to the wall of the ventricle. There is usually a 

 smaller lobe at each angle of junction of the two principal segments, 

 more apparent than those between the segments of the tricuspid valve. 



As on the right side, the two sets of chordee tendinete from the 

 papillary muscles proceed each to an angle between the two segments, 

 and are attached in like manner to their margins and ventricular sur- 

 faces (fig. 173, B, e, e), so that the musculi papillares, when they 

 contract, tend to bring the edges of the flaps together. The chordae 

 tendineffi are stronger and less numerous than in the right ventricle. 



The arterial or aortic orifice circular in form, and smaller than the 

 auricular, is separated from it only by the attachment of the anterior 

 segment of the mitral valve. 



As in the pulmonary artery, its valve consists of three semicircular 

 flaps {semilunar ox siginoid,) (fig. 172, II) each of which is attached by its 



Fi'T. 172. 



II 



Fig. 172. — The Sejiiltjnar Valves of the Aorta and Pulmonary Arterv, seen 

 FROJi their Distal Side (Allen Thomson). 



I, transverse section of the pulmonary artery immediately above the attachment of the 

 semilunar valves : «, the left, ami c, the right anterior segments ; h, the posterior 

 segment : opposite each the sinus of Valsalva is seen, and between tliem the attachment 

 of the valve-segments to the inner wall of the artery. 



II, a similar section of the aorta : a, the left posterior segment, and h, the anterior 

 segment, with the corresponding sinuses of Valsalva, from which the coronary arteries 

 are seen to take their origin ; c, the right posterior segment ; (/, the posterior, and e, 

 the anterior coronary arteries. * 



A, in each case, as in tig. 171. 



convex border to the side of the artery at the place where it joins the 

 ventricle, whilst its other border, nearly straight, is free, and projects into 

 the interior of the vessel. The segments are composed of duplicatures 

 of the endocardium, and of enclosed fibrous structure, which varies in 

 thickness at different parts. A tendinous band strengthens the free 

 edge of the valve, and at the middle of that margin there is a slight 



* As a result of the study of sections made from frozen bodies, it would appear that the 

 above nomenclature most correctly descrilies the natural position of the valve-segments. 

 Those of the pulmonary valve are, however, more commonly known as an anterior, a, and 

 two posterior ; those of the aortic, as a posterior, c, and two anterior. 



