90—56 INDIAN TERTIARY AND POST-TERTIARY VERTEBRATA. 
second incisor, and its crown was in all probability not produced much above the 
level of the incisors : it is in immediate contact with iTli, the base of the latter being 
indented by the canine. The incisors are all much worn ; and are directed 
considerably more upwardly than in Sus. The first incisor (i. l) is a narrow 
compressed tooth, of much the same form as in that genus. The second incisor is 
much larger than the first, and its crown is greatly expanded laterally towards the 
summit : in general form it is more like the corresponding tooth of a ruminant than 
of Sus. The third incisor is considerably smaller than the second, but had a 
similarly expanded crown, and is likewise more like the corresponding tooth of a 
ruminant than a pig. In the absence of any diastema the present specimen 
resembles TTyotherium^ ; as it does in the expanded crown of 175, and the curved form 
and upward direction of all the incisors. The large size of 172 and its expanded 
crown are, however, characters not found in Ilyotherium ; and are very decided 
ruminant characters. The form and direction of the incisors clearly indicates that 
Hippohyus was an animal more adapted for grazing than the true pigs ; — a conclusion 
fully borne out by the characters of the molars. 
Affinities. — The foregoing comparisons indicate pretty conclusively that the 
present form is generically distinct from Sus. In certain cranial characters, and in 
the arrangement of the teeth the genus shows strong indications of affinity with 
Hyotherium. In the structure of its molars it is, however, widely different from that 
genus ; sj^ecies of Sus with comparatively simple molars, like S. titan, occujDying in 
this respect a middle position between Ilyotherium and Hippohyus. The true molars 
present a very considerable resemblance to those of Hippopotamus, but are widely 
distinguished by the equal development of the longitudinal and transverse valleys, 
in place of the diminution of the former and the enlargement of the latter. There 
is a distant resemblance to the molars of the horse in those of the present genus, 
which cannot, however, be taken to indicate any affinity between the two : if the 
generic name was assigned from this resemblance it is a highly objectionable one. 
In another direction the molars of Hippohyus make a decided approach to those 
of some of the selenodont Artiodactyla. Thus if the upper molars of simjfie 
selenodonts like Hemimeryx or Hyopotamus^ be compared with those represented in 
plate XII., fig. 17, it will be seen that the plan of structure is essentially the same 
in the two ; the median columns a, g, h, in the Hippohyus molar corresponding to the 
extremities of the crescents of the selenodont tooth. The molars of Hippohyus are, 
however, less like those of the ruminants than are those of Hemimeryx, and are of 
far too complex structure to be on the ancestral line of that genus ; whence it is 
probable that Hippohyus may be regarded as an offshoot from a pig-like stock which 
has died out without descendants. 
Distribution. — Remains of Hippohyus have been obtained from the typical 
Siwalik Hills and from the Punjab. The smaller form comes solely from the 
Punjab. 
1 Vide Filhol, ‘ Ann. Sci. Geol.,’ vol. XI., pp. 21-3, pi. VII. 
2 Supra, vol. II., pi. XXIII. 
