XIII SABRE-TOOTHED TIGERS 4OI 



form is sometimes, though quite unnecessarily, separated as C. 

 lanigcra. The genus occurs fossil in the Siwalik deposits of 

 India, the species being known as 0. hrac]iygnaf]i<(. 



Fam. 2. Machaerodontidae. — This is a family of totall}- 

 extinct Cats which range from the Eocene 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, thei'e is a postglenoid foramen. 

 There is also a distinct carotid foramen, wdiich 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 tlie 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 Proaelurvs, 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 Cryftoproda. has been 

 insisted upon. ArchaeluTus has suffered a reduction, since one 

 premolar in the lower jaw has disappeared, its formula lieing thus 

 I I C ^ Pm I M ^. The next stage is shown by Dinictis with 

 three premolars in l)otli 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 probal)ly plantigrade. It 

 had retractile claws. 



In the genus Nimravv.s the dental formula is still further 

 reduced. Another premolar of the lower jaw has gone, the 

 formula being thus 1 1^ C -]- Pm | M ^. JVimravus 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 



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