197 
of Edinburgh, Sessio7i 1863-64. 
of the vessels. In the Keptile, where the circulation is also lan- 
guid or slow, the shape of the ventricle or ventricles,* and of the 
ventricular cavity or cavities, is conical ; the cone being slightly 
twisted upon itself. As the muscular fibres forming the ventricle 
pursue a more or less spiral course, and this arrangement extends 
to the valves, their action may be aptly compared to that which 
obtains in the valves of the largest veins, and in those of the 
arteries. It is, however, in the auriculo-ventricular valves of the 
Bird and Mammal that the spiral action of the segments becomes 
most conspicuous ; the nature of the action being unavoidably de- 
termined by the spiral arrangement of the muscular fibres forming 
the ventricles, and by the spiral nature of the musculi papillares 
and ventricular cavities. As the two spiral musculi papillares 
project into the spiral ventricular cavities, it follows that between 
them there exist two spiral grooves or depressions, and in these 
the blood is arranged, on its entrance into the ventricles, in two 
spiral columns ; that fluid, towards the end of- the diastole and 
the beginning of the systole, advancing on the segments of the 
auriculo ventricular valves in spiral waves, from below upwards, 
and wedging and screwing them into each other in an upward 
spiral direction ; the musculi papillares, by contracting, dragging 
the segments towards the end of the systole, by means of the 
chordae tendineae, in an opposite or downward direction, to form a 
spiral dependent cone, the apex of which points to the apex of the 
heart. The action of the auriculo ventricular valves is partly 
mechanical and partly vital, the musculi papillares and analogous 
structures exercising, through the chordm tendineae, at one time a 
restraining influence to prevent retroversion and regurgitation, at 
another wielding a direct power for approximating and applying 
them accurately to each other. The paper, which is based on an 
extensive series of dissections, is illustrated by upwards of 50 
photographs and drawings, showing the structure, relations, and 
action of the valves. 
^ In some cases, as is well known, the almost perfect septum divides the 
ventricle into two. 
