394 ANGIOLOGY. 



ing resembles the right in structure, and is guarded by a valve 

 with two cusps, the bicuspid or mitral valve. The cusps consist 

 of doublings of the lining membrane, strengthened with fibrous 

 tissue, and, it has been said, by muscular fibre. One cusp rests 

 between the auriculo-ventricular and aortic openings ; the other, 

 larger and freer, is opposite. They surround the opening, their 

 sides being attached for a short distance, their apices separate. 

 The musculi papillares of the left side are two, corresponding to 

 the valve segments ; they are large and prominent, one anterior, 

 the other posterior. The chordae tendineae are few, longer, and 

 more powerful than those of the right side ; they are attached 

 to the flaps in a similar manner, and spring from the musculi 

 papillares. 



The aortic opening is deeply situated in the supero-anterior 

 part of the ventricle, a little to the right of the auriculo-ventricular 

 opening, from which it is separated by one of the segments of the 

 mitral valve. It is guarded by three semilunar valves, which 

 are similar in shape and appearance to, but thicker and stronger 

 than those of the right side ; the corpora Arantii are larger and 

 better developed, the sinuses of Valsalva deeper. From two of 

 the latter spring the coronary arteries, which supply the substance 

 of the heart with blood. 



The septum of the ventricles is triangular in shape, and 

 extends to the apex of the heart. It is thick at the base, 

 thinner at the apex ; convex in the right ventricle, concave in 

 the left. 



STRUCTURE OF THE HEART. 



The heart consists of a fibrous framework, muscular and con- 

 nective tissue, vessels, and nerves, the whole being covered by one, 

 and the cavities lined by another, serous membrane. The fibrous 

 frameiuorh consists of fibro- cartilaginous rings placed around 

 the auriculo-ventricular and arterial openings, extending within 

 the doubling of lining membrane which forms the valves and 

 chordae tendinese ; they are strongly developed on the left side. 

 The auriculo-ventricular rings divide the heart into two distinct 

 parts, an auricular and ventricular ; they are thicker on their lower 

 edge, whence spring the muscular fibres of the ventricles, the 

 mitral and tricuspid valves, while from the upper edge arise the 

 muscular fibres of the auricles. The right margin of the left 

 auriculo-ventricular ring is connected with the ring surrounding 



