354 
POPULAR SCIENCE REVIEW. 
side next the ventricle, but principally along their margins, 
where there is the greatest danger ot‘ their being forced through, 
and the other ends of these tendons are united to the ends of 
muscular bands like those which help the contraction of the 
ventricle, the other ends of these bands being fastened to the 
wall of the ventricle, — so that they actually hold the valves like 
ropes, and so prevent them going through into the auricle : of 
course, these ropes, so to call them, must shorten as the 
ventricle contracts, and its wall comes near the opening, since 
otherwise they would not be tight, and would consequently be 
useless, and this is accomplished by the muscular bands con- 
tracting at the same instant with the ventricle itself, so that the 
tendinous threads are always kept tight, and the muscular 
bands relax themselves, and consequently lengthen, as the 
ventricle dilates, for, otherwise, they would tear the valves 
completely off their attachments. Thus we see the advantage 
of having these checks on the valves composed partly of tendon, 
which will not shorten nor lengthen, and partly of muscle, which 
will do so ; for if they were all of tendon they would not con- 
tract nor remain tight, and the valves would be forced through, 
and if they were altogether of muscle the contraction would be 
too great, and would draw the valves inwards, so that they 
could not completely close, and the blood would regurgitate. 
There is, however, another very beautiful arrangement here 
to prevent the blood being forced in too great quantity into the 
delicate vessels of the lungs during violent exertion, as this 
would rupture them, — a result which sometimes takes place in 
spite of the contrivance to avoid it, and hence we sometimes 
see runners and others spit blood after violent exertion. 
This contrivance consists in having one of the muscular 
bands mentioned above very long, but placed nearly opposite 
the valves, so that though there is very little tendon attached to 
it, yet during a contraction of the ventricle the other end is 
brought so close to the valves that it does not draw them 
inwards nor prevent their complete closure ; but if the ventricle 
should ever become too full, so as to endanger the lungs, then 
the other end of this muscle, being attached just opposite the 
valves, is drawn away a long distance from them, so that when 
this muscular band contracts it does draw the valves inwards, 
and allows the blood to regurgitate into the auricle, and from it 
into the great vein which comes from the upper part of the 
body, and so the pressure is taken oft" the lungs. Hence it is 
that the veins of the neck and face become distended during 
exertion ; and the same thing is seen to take place during a 
prolonged note in singing, for then the blood does not pass so 
freely through the lungs, and this safety-valve action, as it is 
called, is brought into play. It was to this we referred when 
