J32 MAMMALIA ORDER VI.UNGULATA. 



met with having two pairs of these teeth on one side of the jaw. If fossil 

 species be taken into consideration, other variations will be found in the 

 number of these teeth ; but before proceeding farther, it is necessary to 

 remark that, since in ordinary Mammals the typical or full complement of 

 incisor teeth consists of three pairs, it is natural to suppose that one pair has 

 been lost in the common species. That such is the case is demonstrated by 

 the extinct Siwalik hippopotamus (H. sivalensis) of the Himalaya, in which, 

 between the two large tusks, there are three pairs of incisors, differing from 

 those of the common species in being all of nearly equal size ; and if we were 

 to examine the upper jaw, we should find the same number of teeth. In the 

 presence of these three pairs of incisors the Siwalik hippopotamus resembles 

 the pig, from which it departs less widely than does the common species, in 

 that these teeth are relatively smaller, and also of nearly equal size. The 

 Siwalik hippopotamus must accordingly be regarded as a less specialised 

 species than either of its living cousins ; and since, together with an allied 

 species from Burma (H. iravaticus), it is the oldest representative of the 

 genus, its generalised features are precisely what evolutionary considerations 

 would have led us to expect. There is, however, yet another point in con- 

 nection with these teeth demanding notice. From the evidence of the 

 common species, it is impossible to determine which of the three pairs of 

 lower incisors found in the Siwalik hippopotamus have dissappeared in the 

 former ; but in the gravels of the Narbada Valley in Central India, there are 

 found two extinct members of the genus, H. namadicu-s and H. pal&iiidicitg, 

 in the former of which 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 about to disappear altogether. There is thus evi- 

 dence that the missing pair of lower incisor teeth in the common hippopota- 

 mus is the second ; and 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 quite possible that the African hip- 

 popotamus may have been derived from the Siwalik species, it is clear that 

 the pigmy hippopotamus is not the descendant of its giant existing cousin. 



With regard to the geographical distribution of the genus, while there is 

 no evidence that the pigmy species ever ranged beyond its present habitat of 

 Liberia, the case is very ditFerent with regard to the range of the common 

 species. At the present day this animal is found from the Cape Colony 

 northwards to the cataracts of the Nile, and it extends westwards to Senegal; 

 but while for several centuries it has been very seldom met with on the 

 Nile below the entrance of the Atbara and Blue Nile, there is abundant evi- 

 dence that in the time of the Pharaohs it was common in Egypt, where in 

 the temple of Edfu, as well as several other buildings, there are frescoes re- 

 presenting the mode in which it was hunted and speared. That the hippo- 

 potamus is the animal indicated in the book of Job under the name of 

 behemoth is undoubted, but there is no evidence that the Jews were 

 acquainted with it otherwise than during their sojourn in Egypt. It is true 

 it has been suggested that its range may have extended eastwards as far as 

 Palestine, but this is conjecture, and, had the creature ever lived there, some 

 of its remains should have been found. In the superficial deposits of Southern 

 and Central Europe there occur, however, numerous remains of a hippo- 

 potamus which cannot be specifically distinguished from the existing African 



