ANATOMY OF THE BEAVER. 
555 
plete, constituting only a semicircle, and can never shut 
the orifice of the vein against the reflux of blood from the 
right auricle. From these observations, I have been long 
in the habit of considering these semi- valves as quite ana- 
logous to the other valves of the venous system; but I 
readily admit, that much more extended researches into 
the comparative anatomy of these organs are required, be- 
fore the physiologist can venture to decide on their funq^ 
tions. 
