OSTEOLOGY OF THE HYOPOTAMIDGL 
75 
belong all the existing Suina and the Hippopotamus ; to the second, the remaining 
Paridigitata, which all possess, more or less completely, the faculty of rumination 
coupled with the absence of incisors (Camel "?) in the premaxillaries. Such a division 
of Paridigitata would allow a place in the zoological scale to the extinct forms which 
were distinguished by the non-confluent metapodium, and the presence of incisors in the 
premaxillaries, and very probably did not ruminate. 
We shall now proceed to cast a comparative glance at the structure of the feet in 
both these divisions as they exist in our own time, and endeavour to discover if their 
structure does not present some characters which show that they are better adapted for 
new circumstances of life than were their Eocene and Miocene predecessors; and that 
to this better adaptation may be, in part, ascribed the victory they obtained in the battle 
of life, and their spreading over all the surface of the globe. 
As the Paridigitata with tuberculated teeth are represented, in the recent period, 
only by the Suina, and those with crescentic teeth only by the Euminantia, we shall 
have to confine ourselves to these two orders ; in the latter we shall particularly call 
the attention of the reader to the Tragulina, as the less reduced members of this 
family, and therefore more likely to furnish us with typical characters. 
The true Suina have four complete digits in their manus and pes, but only the two 
middle ones are subservient to the purpose of locomotion ; the laterals are always so 
reduced that they do not regularly touch the ground, or only do so on muddy soil, when 
the foot sinks deeply into the earth. According to the general rule laid down for all 
the Paridigitata, the interlocking of the two middle (third and fourth) metacarpals in 
the manus is effected as usual ; the fourth digit is supported by the unciform, while its 
radial upper margin is fitted into an excavation on the ulnar side of the third metacarpal, 
which, by means of an ulnar process of its upper margin, articulates with the unciform, 
while its proximal surface is supported by the os magnum (see figs, in Cuvier, ‘ Oss. Foss. 
Atlas,’ and He Blainville, ‘ Osteograpliie, Sus,' also our fig. 4, Plate XXXVII.). How- 
ever, in examining more attentively this proximal surface of the third metacarpal of 
the Hog, we remark something quite new, and not met with in most of the fossil 
Paridigitata. Owing to the over-development of the middle digits, the radial side of 
the third metacarpal (Plate XXXVII. fig. 4) has spread inwards and pushed the 
second metacarpal away from its typical articulation with the os magnum ; nay even 
more, this second metacarpal has yielded one half of the surface of its carpal bone 
to the encroachment of the third digit ; this last, besides the magnum, occupies 
now one half of the trapezoid — a new fact in the history of the Paridigitate foot 
that had important consequences. To show the reader more clearly that this modifica- 
tion is a recent one, we turn to the fossil Suidge. Unhappily, our knowledge of their 
skeleton is very imperfect ; and while genus after genus (not to speak of species) of the 
fossil Suidse have been created merely on dental, often very slight and unimportant, 
characters, the study of their skeleton has been much neglected. As far as I am aware, 
MDCCCLXXIII. M 
