358 EXISTENCE OF VALVES IN THE PULMONARY VEINS. 
These cases — and others we could adduce — are, after all, how- 
ever, to be regarded but as the exceptions to the laws of Nature ; 
and happily for us they are too few and far between to insubstan- 
tiate those rules by which we profess to tell age by the number, 
the kind, and the aspect of the teeth. Having thus briefly sketched 
an outline of the opinions we hold on this highly interesting sub- 
ject, — one to which we shall at another time recur, — we hope to 
hear, and shall feel most happy to hear, the results of the obser- 
vations of others, it being by actual observation alone, on an ex- 
tensive and varied scale, that we can at the last come to sound 
practical conclusions. 
MISCELLANEA. 
On the Existence of Valves in the Pulmonary Veins. 
We find it stated in most anatomical works, that the pulmonary 
veins possess no valves. My attention, says Professor Mayer, of 
Bonn, was first directed to the presence of valves in the pulmonary 
veins when carefully examining the lungs of an ox, in which animal 
valves not only exist, but in a considerable number. I examined, at 
the same time, the lungs of a pig, and found them entirely wanting. 
In the human lungs, however, they are both large and numerous, and 
it is a matter of astonishment that their existence could have been 
overlooked. There is always a valve, for instance, in the spot where 
a collateral branch opens, at an acute angle, into the trunk of the 
pulmonary vein. The valve is apparent in proportion to the acute- 
ness of the angle at which the vein opens ; but there are no valves 
in the pulmonary veins at those spots where the collateral branches 
open at a right angle : this is also the case in the whole of the ven- 
ous system. In the veins of the extremities, valves are to be found 
where the collateral branches open at an acute angle, but never 
where they enter into the main trunk at a right angle. This will 
account for the valves in the pulmonary veins being less numerous 
than in the other veins, as the collateral branches open principally 
at a right angle. This mode of communication is particularly evi- 
dent in the pig, and in this animal the pulmonary veins have no 
valves. — Tiedemanns Zeitschrift fur Physiologie. 
