8 THE BEAVER 
tooth is used the dentine wears away much faster than the 
enamel, with the result that there is always a chisel edge at 
the front of the tooth. During the life of the animal these 
teeth continue growing, and if by any chance there is an 
injury to a tooth so that it no longer opposes the one in the 
opposite jaw, the latter may keep on growing until it is of 
such a length as to be a source of great trouble to the owner 
even if it does not cause death from starvation from inabil- 
ity to feed. The color of the front of the incisors is a 
bright orange-red. ‘They are long, and the concealed por- 
tions are much curved in the skull and lower jaw. Morgan 
gives the radius of the curve of the upper incisors as one 
inch, and of the lower 12 inches. I obtained somewhat 
different results in the case of the teeth I] measured, these 
radii being 0.6 and 1.6 inches respectively. Very likely my 
specimens were from a smaller animal than Morgan’s (Figs. 
3 and 4). 
There are four teeth in the molar series on either side of 
each jaw, formed of alternate vertical layers of enamel and 
dentine, which by their unequal wear always afford a good 
grinding surface. 
The muscles on the side of the head wish actuate the 
jaws are thick and powerful, as they need to be to enable 
the animal to do the work it does with its teeth, such as 
gnawing wood, tearing out chips, and dragging sticks and 
logs. 
Adult beavers range in weight from forty pounds up- 
ward. A sixty-pound one is an unusually heavy one, while 
seventy pounds is very rare, though Bailey states there are 
records of old and very fat beavers weighing 100 to 110 
pounds. He gives the weight of two two-weeks old beavers 
at 12 and 2 pounds respectively. 
The genital organs are beneath the skin, protected from 
the water, and open into the anal cloaca, hence one cannot 
