THE VALVES. 



307 



would otherwise force them back through the auricular orifice ; the papillary 

 muscles, shortening as the cavity of the ventricle itself is contracted during 

 its systole, are supposed thus to prevent the valves from yielding too much 

 towards the auricle, which might have been the case had the chordae ten- 

 dineee been longer, or fixed directly into the wall of the ventricle. The 

 middle part of each segment is thicker than the rest, whilst the marginal 

 part is thinner, more transparent, and jagged at the edges. In the angles 

 between each pair of the principal segments of the atiriculo- ventricular valves 

 there may be found, but not constantly, as many small intermediate lobes. 

 The musculi papillares are arranged in groups as many as there are seg- 

 ments of the valve, and the chordae tendineae from each are distributed 

 to the adjacent sides of two different valves, so as to draw their margins 

 together, 



According to Kurschner (Wagner's Handwb'rterbuch, art. " Herzthatigkeit "\ three 

 kinds of cords belong to each segment : a, the first set, generally two to four in number 

 and proceeding from two different sets of papillae, or from one of these and the 

 wall of the ventricle, run to the base or attached margin of the segment, and are 

 there connected also with the tendinous ring round the auriculo-ventricular opening ; 

 b, the second set, more numerous, and smaller than the first, proceed also from two 

 adjacent papillary muscular groups, and are attached to the back or ventricular surface 

 of each segment at intervals along two or more lines extending from the points of 

 attachment of the tendons of the first order at the base of the valve to near its free 

 extremity ; c, the third set, which are still more numerous and much finer, branch 

 off from the preceding ones, and are attached to the back and edges of the thinner 

 marginal portions of the valves. A few muscular fibres prolonged from the 

 neighbouring walls penetrate into the segments of the auriculo-ventricular 

 valves. 



Fig. 231. 



Fig. 231. THE SEMILUNAR VALVES OF 

 THE AORTA. AND PULMONARY ARTERY, 



SEEN FROM THEIR DlSTAL SlDE. 



A, transverse section of the pulmonary 

 artery immediately above the attach- 

 ment of the semilunar valves : a, the 

 anterior segment ; &, the left, and c, the 

 right posterior segments : in each the 

 sinus of Valsalva is seen, and between 

 them the attachment of the ends of the 

 valve- segments to the inner wall of the 

 artery. 



B, a similar section of the aorta, 

 showing the semilunar valves from their 

 distal side : a, the left, &, the right 

 anterior segments, with the sinuses of 

 Valsalva, from which the corresponding 

 coronary arteries are seen to take their 

 origin ; c, the posterior segment ; d, 

 the right, or posterior ; 0, the left, or 

 anterior coronary arteries. 



The semilunar or sigmoid valves, 

 placed at the mouths of the aorta 



and pulmonary artery, consist of three semicircular folds, each of which is 

 attached by its convex border to the side of the artery at the place where 

 it joins with the ventricle, whilst its other border, nearly straight, is free, 

 and projects into the interior of the vessel. They are composed of dupli- 



