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 (A. namadicus), and 
the other as the Indian hippopotamus (A. 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 
