EXTINCT FORMS. 
5i5 
transition from the molars of the anchithere to those of the earlier horses. Further, 
the lateral toes of the anchithere, as shown in the figures on p. 153, were relatively 
larger than in the three-toed horses. Moreover, in the anchithere, the radius and 
ulna in the fore, and the tibia and fibula in the hind-limb, were perfectly distinct 
and fully-developed bones. The largest anchithere approached an ordinary pony 
in size, while the smallest was not larger than a sheep; and in all these animals 
there was the full typical number of forty-four teeth, while the “ mark ” character¬ 
istic of the incisors of the horse was but faintly indicated in one species alone. 
Passing downwards in the geological scale, by a complete transition from the 
anchithere, we arrive in the lower Eocene London Clay at a small animal known 
as the hyracothere, which was not larger than a fox, and had four toes to the front, 
and three to the hind-feet; while the forty-four low-crowned teeth were of still 
simpler structure than in the anchithere, although formed on the same general 
plan. The last lower molar tooth of the hyracothere differs however from that of all 
existing Odd-toed Ungulates in having three complete lobes, and thus approximates 
to the corresponding tooth of the Even-toed group; and it may be added that the 
essential correspondence in the structure of the upper molars of the two groups 
will be apparent by a comparison of the figure of the molar of the anoplothere on 
p. 421, with that of the anchithere on p. 487. 
A step from the hyracothere brings us to the still earlier phenacodus, in which 
each foot, as shown in the figure on p. 8 of the first volume, had five complete 
toes; while the molar teeth had their crowns with small isolated tubercles instead 
of ridges. This small primitive animal, with a most generalised type of structure, 
appears then to be the undoubted ancestral stock from which the modern horse 
has been slowly produced by some process of evolution, which was going on through¬ 
out the long ages of the whole Tertiary period; and it is at least noteworthy that 
the true horse only made its appearance on the globe at or about the same time as 
his master, man. 
Paiseotheres and In addition to the animals referred to above, as forming the direct 
LopModons. ancestral line of the modern horse, there were a number of other more 
or less closely-allied types belonging to the Odd-toed group. Among these some of 
the best and longest 
known are the palseo- 
theres, from the upper 
Eocene strata of Europe, 
of which, as far back as 
the early portion of the 
present century, nearly 
complete skeletons dis- 
r . THE LEFT UPPER CHEEK-TEETH OF THE GREAT PALiEOTHERE 
■COVered in the gypsum (J. nat. size).—After Gaudry. 
quarries, near Paris, 
were described by Cuvier. These palseotheres were tapir-like animals, with three 
toes to each foot, and molar teeth approximating to those of the anchithere in 
structure, but having a somewhat elongated neck. While some of the species were 
not taller than a sheep, others must have fully equalled the largest tapirs in size. 
They probably resembled the tapirs in having a short proboscis to the snout, and 
