114 FAMILY CHARACTERISTICS. 
while the Seal has a continuous uniform outline 
adapted for swimming. They form separate 
Families, and are easily recognized as such by the 
difference in their external outline; but what is 
the anatomical difference producing the peculiar- 
ity of form in each, by which they have been 
thus distinguished? It lies in the structure of 
the-limbs, and especially in that of the wrist 
and fingers. In the Seal the limbs are short, and 
the wrists are on one continuous line with them, 
so that it has no power of bending the wrist or 
the fingers, and the limbs, therefore, act like flap- 
pers or oars. The Bear has a well-developed paw 
with a flexible wrist, but it steps on the whole 
sole of the foot, from the wrist to the tip of the 
toe, giving it the heavy tread so characteristic of 
all the Bears. The Dogs, on the contrary, walk 
on tiptoe, and their step, though firm, is light, 
while the greater slenderness and flexibility of 
their legs add to their nimbleness and swiftness. . 
By a more extensive investigation of the anatom- 
ical structure of the limbs in their connection 
with the whole body, it could easily be shown 
that the peculiarity of form in these animals is 
essentially determined by, or at least stands in 
the closest relation to, the peculiar structure of 
the wrist and fingers. f 
Take the Family of Owls, as distinguished 
from the Falcons, Kites, ete. Here the differ- 
