212 BRITISH MAMMALS 



Although the Duplicidentata are strongly represented in India 

 and Central Asia, the balance of proof seems to be in favour of 

 their having originated (perhaps with the whole of the Rodentid) 

 in North America. Not only is a species of pika found still 

 living in that continent, but on a mountain in Mexico a primitive 

 type of rabbit-like Rodent has been recently discovered, the 

 scientific name of which is Romerolagus . Lastly, hares are 

 abundantly represented in both North and South America, and in 

 both North and South America occurs the form of hare most 

 nearly related to the rabbit. 



The Leporida are, all things considered, the most primitive of 

 Rodents and of the Duplicidentata. They possess two permanent 

 incisors on each side of the upper jaw, and in young animals a 

 third incisor occurs in the " milk " dentition. There are three 

 pairs of premolars in the upper jaw, and two pairs in the lower. 

 The molars are three pairs in both jaws, the third molar being 

 very small. All the molars are rootless, and their crowns are 

 marked with transverse ridges of enamel. The fore feet are 

 five-toed, the hind limbs four-toed. The ear conch is invariably 

 long, sometimes very long. 



The hares and rabbits are now generally divided into two 

 distinct genera, Oryctolagus and Lepus, because there are dif- 

 ferences in structure and habits between the true hares and the 

 common rabbit, which are thought to be of generic importance, 

 even though one or two intermediate forms exist which it is very 

 difficult to classify as belonging precisely to either group. 



Oryctolagus cuniculus. The Common Rabbit 



This creature is perhaps the only type of the genus Oryctolagus 

 which, although connected by intermediate forms, differs in the 

 following particulars from most hares of the genus Lepus : 

 the longer and narrower bones of the palate, the more slender 

 muzzle, the smaller size and capacity of the skull, the shorter 

 ears (nearly without the hares' black tips), and the condition of 

 the young at birth — these in the rabbit being naked and but 

 poorly developed, while the young of hares are born with their 



