CIVETS, MACHAIRODONTS, AND CATS 169 



with his weapons and cunning. The Machairodonts are closely 

 related in origin to the True Cats, though, on the one hand, they 

 exhibit more generalised features in their structure, and, there- 

 fore, cannot be derived from the existing cats ; and, on the other, 

 their dentition shows great specialisation. The general structure 

 of the skeleton is remarkably like that of the Cats, but at the base 

 of the skull there is an alisphenoid canal, together with other 

 features (postglenoid and carotid foramens) of a primitive character 

 lost in the True Cats. The femur, or thigh bone, also retains 

 the third trochanter, a feature which is entirely lost in the 

 True Cats. 



In their dentition the Machairodonts begin as very generalised 

 cats with a tooth formula of three pairs of incisors in each jaw, 

 one pair of canines, four pairs of premolars in the upper jaw and 

 three in the lower, and one pair of molars in each jaw. But in 

 the genus Eusmilus the teeth were reduced to three pairs of 

 incisors in the upper and only two pairs in the lower, while in the 

 upper jaw there were only two pairs of premolars and a single 

 pair of molars, and in the lower jaw one pair of premolars and 

 one pair of molars. The canine teeth through all this family 

 or sub-family were gradually developed to enormous size and 

 trenchant capabilities, so that in the grandest examples the upper 

 canine may well be compared to a sabre, as it is broad, flattened, 

 thin, and has a finely serrated edge. The great tusks of the 

 sabre-toothed "tigers" differ, indeed, from most developments of 

 tusk-like canines (except in the case of some extinct Ungulates) in 

 their very small diametrical measurement. They are broadened 

 and flattened out like the blade of a scythe. Curiously enough, 

 the most specialised Machairodont (so far as dentition is concerned) 

 appears very early in geological history. This is the genus 

 Eusmilus^ which makes its appearance in the Upper Eocene. It 

 may even have reached Britain, though no traces of it have yet 

 been discovered. This is admittedly one of the problems of 

 palaeontology. It is not until the Upper Eocene that any traces 

 whatever of True Carnivores are found. At this stage we find 

 ancestral forms of the Cats, Civets, and Dogs, yet at the same 



