196 Proceedings of the Boyal Society 
bands which run between the segments and afford a certain degree 
of support. The action of the valves in fishes is partly mechanical 
and partly vital, for we must regard the contraction of the bulb as 
contributing to the closure. In the auriculo-ventricular valves of 
mammals, birds, reptiles, and fishes, we have a great variety. 
These valves are characterised by the presence of tendinous 
chords (chordee tendinese) which connect them with actively con- 
tracting muscular structures ; as, the interior of the ventricles 
or the structures arising therefrom — viz., the carnese columns and 
musculi papillares. They therefore differ from the semilunar 
valves proper. In the auriculo-ventricular valves there is also gra- 
dation. In some instances, e.g.^ there is only one semilunar flap 
or segment ; in a second there are two flaps or segments, so 
arranged that their long diameters correspond to the direction of the 
muscular fibres with which they are connected directly. In a third, 
the two segments are attached to the interior of the ventricle by 
rudimentary chordae tendinece. In a fourth, two accessory or 
smaller segments are added to the two principal ones, the whole 
being attached by well-developed chordae tendinece to rudimentary 
musculi papillares. In a fifth, which is the most perfect form of 
valve as it exists in man, and in the higher mammalia, the seg- 
ments are from four to six in number, most exquisitely and symme- 
trically formed^ and attached by minutely graduated chordae tendinece 
to highly developed carnece columnce and musculi papillares ; the 
latter being distinctly spiral. 
The action of the auriculo ventricular valves is varied, and 
depends on the circulation, on the configuration of the ventricles, 
and the shape of the ventricular cavities, which adapt and mould 
the blood, and cause it to act in a definite or given direction. In 
the Fish, the ventricle and the ventricular cavity are pyramidal in 
shape, the ventricular fibres being so arranged that the organ con- 
tracts and dilates very much as one would shut and open the hand. 
As, moreover, the circulation is languid, the segments of the valve, 
when two exist, are forced towards each other, by the contraction of 
the ventricle and by the blood, in a manner analogous to that by 
which the segments of the bisemilunar venous valves are approxi- 
mated, by the retrogressive movements of the slowly advancing 
venous blood, assisted to a slight extent by the vital contractility 
