228 
POPULAR, SCIENCE REVIEW. 
The food of our English hats consists of insects, and their 
teeth bristle with sharp points, well suited to pierce the chitinous 
cases by which the bodies of insects are protected. 
The stomach (like that of most beasts which live upon a 
purely animal diet) is a simple, short and rounded bag. 
The female is provided with a pair of milk glands, situated 
on the breast — as in the apes and in man. 
The skeleton of the bat, when compared with those of some 
other animals, affords an excellent example of how fundamental 
uniformity of structure may underlie forms which are strikingly 
different — in accordance with diverging habits of life. 
I have already called attention to the divergent aspects of the 
aerial bat and the subterranean mole. Yet the bones of the 
flying organ of the bat closely re- 
semble that of the burrowing organ of 
the mole, save as regards the relative 
shapes and dimensions of the compo- 
nent bones. But while in the bat these 
bones are drawn out into excessive 
length and tenuity, in the mole they 
exhibit the maximum of concentration 
and robustness. Now both these con- 
ditions are but diverging manifestations 
of the human structure, and the same 
indeed may be said of such extreme 
modifications as the fore-leg of the 
horse or the paddle of the whale. 
But the bat and the mole present 
us with a special point of similarity in 
their skeleton not found in the other 
animals named, including ourselves. 
It is that the breast-bone in both 
the bat and mole develops a median 
ridge or keel. This keel serves to 
afford additional surface for the attach- 
ment of powerful muscles which pass 
thence to the arms, and which, in the 
bat, by their contraction, strike the 
wings downwards in flight. 
Everyone present must have observed, when carving a fowl, 
that there is a ridge or keel to the breast-bone, and that a volu- 
minous mass of muscle — the breast of the fowl — is situated on 
each side of such keel. Now, our bat has not got such a mass 
of muscle on each side of the keel of its breast-bone as has the 
bird, and for a very good reason. In the bat, as in ourselves, the 
muscles which antagonise those j ust noticed (and which draw the 
arms away from the breast) are situated in the back ; but in the 
sc, wrist-bones ; jp, bones of 
thumb ; Wj. 4 , bones of 
middle part of hands. 
