ANCIENT AND MODERN HIPPOPOTAMUSES 267 



country in which occur those of the common African species, 

 there are found two extinct members of the genus, one 

 known as the Narbada hippopotamus (//. namadicus), and 

 the other as the Indian hippopotamus (//. palaeindicus). In 

 the former of these the lower incisors are similar in size 

 and number to those of the Siwalik species ; but in the 

 latter, while the inner and outer pairs are very large, 

 there occurs on each side between them a minute and 

 rudimentary tooth, squeezed out from the general line to 

 the upper margin of the jaw, and evidently just about to 

 disappear altogether. We have thus decisive evidence that 

 the missing pair of lower incisor-teeth in the common 

 hippopotamus is the second ; and we further see how a 

 complete transition can be traced, as regards the number 

 of these teeth, from the Siwalik species through the 

 common one to the Liberian hippopotamus. While it is 

 possible that the African hippopotamus may have been 

 directly derived from the Siwalik species, it is quite clear 

 that the pigmy hippopotamus is not the descendant of its 

 giant existing cousin. 



With regard to the geographical distribution of the genus, 

 we have already said that the two living species are confined 

 to Africa, to which it may be added that there is no record 

 of their having ever occurred in the districts lying to the 

 north of the Sahara during the historic period. They are, 

 therefore, essentially inhabitants of what naturalists term 

 the Ethiopian region, although they are quite unknown in 

 the island of Madagascar, which belongs to the same 

 zoological province. So far as I am aware, there is no 

 evidence that the pigmy species ever ranged beyond its 

 present habitat of Liberia, although the case is very different 

 with regard to the range of the common species. At the 

 present day this animal is found from the Cape Colony 



