INTERNAL STRUCTURE OF THE HEART. 



305 



The ventricles, on a great part of their inner surfaces, are covered with a 

 number of irregular rounded muscular bands, named columns carnece, which 

 form quite a net-work in some parts of the ventricle, and may be classified 

 into three kinds. The first kind form merely slightly prominent ridges on 

 the walls of the ventricle, being attached by one of their sides as well as by 

 the two extremities ; the second are adherent by their two ends only, and 

 are free in the rest of their extent ; whilst the third kind form a few 

 bundles, named musculi papillares, which are directed in general from the 

 apex towards the base of the ventricle, in which they are attached to the 

 muscular wall by their broader basis, and tapering more or less at their 

 free extremities give rise to small tendinous cords, chordce tendinece, through 

 which they are connected with the segments of the auriculo-ventricular 

 valve. Each ventricle has two orifices, an auriculo-ventricular and an 

 arterial opening. 



Fig. 22 



Fig. 229. VIEW OP THE BASE 

 OF THE VENTRICULAR PART 

 OP THE HEART, SHOWING 

 THE RELATIVE POSITION OP 

 THE ARTERIAL AND AU- 

 RICULO-VENTRICULAR ORIFI- 

 CES. | 



The muscular fibres of the 

 ventricles are exposed by the 

 removal of the pericardium, 

 fat, bloodvessels, &c. ; the pul- 

 monary artery and aorta have 

 been removed by a section 

 made immediately beyond the 

 attachment of the semilunar 

 valves, and the auricles have 

 been removed immediately 

 above the auriculo-ventricular 

 orifices. The semilunar and 

 auriculo-ventricular valves are 

 in the closed condition. 1, 1, 



the w base of the right ventricle ; 1', the conus arteriosus ; 2, 2, the base of the left 

 ventricle ; 3, 3, the divided wall of the right auricle ; 4, that of the left ; 5, the anterior, 

 5', the posterior, and 5", the left or septal segment of the tricuspid valve ; 6, the anterior 

 or aortic, and 6", the left and posterior segment of the mitral valve. In the angles 

 between these segments are seen the smaller fringes frequently observed ; 7, the anterior 

 part of the pulmonary artery ; 8, placed upon the posterior part of the root of the aorta ; 

 9, the right, 9', the left coronary artery. 



Valves. In order to give to the blood propelled by the contraction of 

 the ventricles its due direction through the arteries, two sets of valves are 

 provided, one of which prevents the regurgitation of blood through the 

 auriculo-ventricular openings into the auricles during the contraction of the 

 ventricles, while the other prevents regurgitation from the arteries back into 

 the ventricles when the contraction has ceased. These valves are mainly 

 formed of folds of the endocardium with some fibrous tissue contained 

 within them. 



The auriculo-ventricular valves are composed of membranous flaps or 

 segments, which are three in number in the valve of the right side, and 

 two in that of the left. At their bases, the several segments are con- 

 tinuous with one another, so as to form an annular membrane attached 

 round the margin of the auricular opening : they are directed downwards, 



