THE EUROPEAN FOX. 
213 
they are enabled to maintain for a great length of 
time by the strength of their muscles and the firmness 
of their sinews. Except in one remarkable species, 
the Hyaena-Dog, which has been separated from the 
rest as a distinct genus, they have five toes on the fore 
feet and four only on the hind, the place of the fifth 
being, however, occasionally marked by a rudimental 
claw. Each of the toes is armed with a thick, short, 
blunt, unretractile claw, quite incapable of being used 
like those of the Cats in seizing their prey, which office 
is in these animals wholly performed by the teeth. 
They are equally incapable of being rendered service- 
able in climbing trees, a feat which only one species, 
the Fenriec of Bruce, is said to perform; and in this 
instance our knowledge of the animal is too slight to 
allow us to ascertain the extent to which this peculiar 
faculty is carried. In all the species the extremities of 
the toes, with the broad callous tubercles placed at 
their base, are the only parts which press upon the 
ground in walking ; and they are consequently as 
perfectly digitigrade as the Cats themselves. 
Of the distinctive characters between the Foxes and 
the Dogs the most remarkable bears a direct relation 
to their difierent modes of life, and seems therefore to 
furnish an adequate ground for their separation. In 
the Dogs, however great the intensity of light to which 
they may be exposed, the iris uniformly contracts around 
the pupil in the form of a circle ; while in the Foxes, if 
observed during the day or under the influence of a 
strong light, it is seen to close in a vertical direction, 
the pupil assuming the figure of a section of a double 
convex lens. The object of this provision is evidently 
to exclude the rays of light in a much greater degree 
than would be compatible with the structure of a cir- 
cular pupil ; and it is consequently only found in those 
