THE HEART. 



507 



Fig. 262. 



provided with a circular membrane, the mitral (or bicuspid) valve, because it is 

 cut into several festoons, of which two are the principal : the one anterior, 

 the other posterior, simulating in their outline the two faces of a bishop's 

 mitre. The anterior festoon is the largest, and is attached to the limit of 

 the two orifices, isolating from 

 the ventricular cavity a diver- 

 ticulum which corresponds, in 

 every respect, to the pulmonary 

 infundibulum. The posterior 

 festoon is applied to the walls 

 of the ventricle. Between these 

 two there are usually two second- 

 ary festoons, making up the 

 total number to four ; fre- 

 quently there is an accessory 

 fold, situated on the right side, 

 and fairly developed ; the valve 

 is then tricuspid, like that of 

 the right ventricle. Sometimes 

 two of these rudimentary folds 

 are found on the left side 

 making five festoons in all. 

 The aortic opening, SO named 1, Cavity of left auricle ; 2, Cavity of appendix 



LEFT CAVITIES OF HEART LAID OPEN. 



auriculae ; 3, Opening of two right pulmonary 

 veins ; 4, Sinus into which left pulmonary veins 

 open ; 5, Left pulmonary veins ; 6, Auriculo-ven- 

 tricular opening ; 7, Coronary vein lying in 

 auriculo-ventricular groove ; 8, Left ventricle ; 

 9, 9, Cavity of left ventricle. a, Mitral valve, 

 its curtains connected by chordae tendinae to 6, 6, 

 Columnae carneae ; c, c, Fixed columnae carnae 

 on inner surface of ventricle ; ', Point of appendix 

 of right auricle. 



because it constitutes the origin 

 of the aorta, is placed in front 

 and to the left of the auriculo- 

 ventricular opening, from which 

 it is only separated by a thin 

 muscular spur, to which is at- 

 tached the adherent border of 

 the great festoon or curtain of 

 the mitral valve. It does not 

 differ in anything from the pulmonary opening, and like it, is provided with 

 three sigmoid valves. 



LEFT AURICLE. As in the right auricle, this forms a kind of cover 

 above the auriculo-ventricular opening. Smooth behind, in front, inwards 

 and outwards, its cavity presents a reticulated cul-de-sac, which occupies the 

 appendix auriculas ; and a superior wall, also reticular, having from four to 

 eight orifices, the openings of the pulmonary veins. These orifices have no 

 valves. (Carneaa column* of the third kind are also present, but chiefly 

 between the two posterior pillars; small ones are very numerous on the 

 . borders and summit of the ventricle. The columns of the second order are 

 simple or ramous, and pass from the angles of union of the walls and the 

 point of the cavity ; others on the posterior wall go to the borders and the 

 interval between the two pillars. The most remarkable are bands extending 

 from one wall to the other, the two principal of which are long, strong, and 

 ramous ; they are fixed, on the one side, to the centre of the great posterior 

 reliefs, and ascend to be implanted, on the other side, into the middle of 

 the anterior wall.) 



4. Structure of the Heart. 



Preparation. Before proceeding to dissect the muscular fibres of the heart, it is 

 indispensable to keep that viscus in boiling water for half or three-quarters of an hour. 

 It should then be immediately immersed in cold water, to prevent the desiccation of the 



