THE PELVIS OF BURROWING MAMMALS 201 
Such action undoubtedly calls for strenuous exertion on the 
part of the hind legs while loosening the earth and again while 
the earth is being pushed out of the tunnel. It also requires a 
broad pelvis in order that the hind legs may be placed well 
apart. This broad pelvis possesses a large pelvic aperture, 
allows more room for the passage of the fetus, and hence the 
loss of the symphysis is less imperative than it would be if the 
pelvis were narrower. 
Seton (09) describes the star-nosed mole (Condylura cristata) 
as piling up the earth as the pocket gopher does, while working 
in moist soil, and as tunneling without throwing up the earth 
in the dryer soil. Anyone who has seen the ridges of earth 
raised up by moles in a garden will realize that they force 
their way through the soil in a manner quite different from that 
of the pocket gopher. And from the length of the tunnels 
which they are capable of making, even in a single night, one 
can well believe that a great deal of force is being continually 
' exerted. This crawling between the earth and pushing it aside 
has a continual tendency to compress the pelvis laterally rather 
than to broaden it, as the action of the pocket gopher tends to 
do. Such a narrow pelvis so restricts the pelvic aperture that 
the loss of the symphysis is imperative to allow the passage of 
the fetus. 
Concerning the shrews, it may be said that their pelvis, so 
similar to that of the moles, though less highly specialized, is a 
result of similar habits. The shrews burrow, though they are 
less strenuous in their operations, confining themselves to the 
surface of the ground and the litter which covers it. Seton refers 
to the habits of the short-tailed shrew (Blarina brevicauda) as 
follows: 
‘The furrowed—sometimes tunneled—track that this animal 
leaves in the snow is the exact expression of its methods and of 
its summer life beneath the leaves and rubbish in the woods.”’ 
From this author’s notes the following quotation is taken 
describing an observation: 
‘“‘Free as a mole in the soil, he drove his sub-leaf gangway 
where he would, and doubtless lived on the country as he went. 
