XIII SABRE-TOOTHED TIGERS 401 
form is sometimes, though quite unnecessarily, separated as C- 
lanigera. The genus occurs fossil in the Siwalk deposits of 
India, the species being known as C. brachygnatha. 
Fam. 2. Machaerodontidae.—This is a family of totally- 
extinct Cats which range from the Kocene down to the Pleistocene. 
Their general structure is like that of the Felidae; but they 
differ in a number of skeletal features. Thus there is an 
alisphenoid canal, and, as in Bears, there is a postglenoid foramen. 
There is also a distinct carotid foramen, which does not occur in 
the true Cats. The teeth are often distinguished by the huge 
size of the superior canines, which are “weapons for penetrating 
wounds, without rival among carnivorous animals.” These must 
have been displayed at the sides of the chin when the mouth 
was closed, and it has even been suggested that the animal 
possessing these exaggerated canines could hardly have properly 
closed its mouth. The lower canines were often on the contrary 
much reduced, and in fact incisor-like. In tracing the series of 
these Cats we find a gradual reduction of the teeth from a more 
nearly complete number down to the specialised dentition of the 
existing Cats. The genus Proaelurus, Miocene in range, had 
four premolars in each jaw, and two molars in the lower and one 
in the upper. This is the greatest number of teeth found in any 
member of the group. 
The resemblance of this genus to Cryptoprocta has been 
insisted upon. Archaelurus has suffered a reduction, since one 
premolar in the lower jaw has disappeared, its formula being thus 
I3CiPm$M4z. The next stage is shown by Dinictis with 
three premolars in both jaws. There are a good many species of 
this genus which are all American and Miocene. This genus has 
five toes upon the hind-feet, and was probably plantigrade. It 
had retractile claws. 
In the genus Mimravus the dental formula is still further 
reduced. Another premolar of the lower jaw has gone, the 
formula being thus 13 C+ Pm3 M4. MNimravus gomphodus 
was a Carnivore about the size of a Panther. It has no third 
trochanter upon the femur, which process is present in the 
corresponding bone of Dinictis. Pogonodon was an _ equally 
large animal in which the premolars were three in each 
jaw, but the molars have become reduced to one in_ the 
lower, as they have in this and other genera in the upper 
VOL. X 2D 
