294 Proceedings of the Boyal Society of Edinburgh. [Sess. 
third molars. The first molar from Oreston evidently belonged to a 
decidedly smaller individual than the molars figured by Owen.* The first 
molar (m. 1) from Oreston having only just come into use, was so slightly 
worn that it was impossible to make out the arrangement of the enamel 
folds. To admit of the pattern formed by the enamel being studied, a 
section was carried across the crown about 5 mm. from the grinding surface.*)* 
As fig. 6 shows, the grinding surface of the internal pillar of this small first 
molar is relatively, as well as absolutely, shorter than in the second and 
third molars (figs. 1 and 2) ; instead of being less than twice the length of 
its pillar as in molar 2, the crown of molar 1 is from before backwards 
nearly three times the length of the grinding surface of its pillar. In having 
a short crown and a small internal pillar, the first molar (m. 1) from 
Oreston differs from the corresponding tooth in Equus fossilis (fig. 3), 
from Equus plicidens, Equus nctmadicus and Equus robustus (fig. 5), 
but more or less closely resembles the first molar of Pliohippus, Equus 
stenonis (fig. 7), and Equus sivalensis (fig. 24). 
In the three-toed Miocene horse Mergchippus the internal pillar (fig. 8) 
is small and nearly circular, but in Pliohippus this internal fold of enamel 
is flattened and the grinding surface is about one -third the length of the 
crown measured from before backwards. During Pliocene and Pleistocene 
times the grinding surface of the internal pillar, in at least some of the 
cheek teeth of the Equidae, increased considerably. In Equus sivalensis 
the internal pillar is decidedly long in molar 2 and molar 3 (fig. 24), usually 
somewhat elongated in premolars 3 and 4, but still short in molar 1 ; 
in Equus namadicus the internal pillar is long in all the six large upper 
cheek teeth. In having the grinding surface of the internal pillar short in 
molar 1 but long in molars 2 and 3, the small Oreston equine agrees with 
Equus sivalensis (fig. 24) of India. As it happens, small teeth resembling 
the small first molar (m. 1) from Oreston have been found in Pliocene or 
Pleistocene deposits in Italy, France, and North Africa. The small equine, 
with small short-pillared molars, which inhabited Auvergne and other 
parts of France in early Pleistocene times, has generally (like the small- 
pillared Italian race) been regarded as a member of the Equus stenonis 
group of species, or known as Equus ligeris. On the other hand, the small 
equine with short-pillared teeth which in Pleistocene times inhabited North 
* As the animal to which the very small first molar from Oreston belonged either died 
or was killed when about a year old, it may have been an unusually poorly developed 
member of its race. 
t For having the small first molar from Oreston sectioned, and for many other obliga- 
tions, I am indebted to Dr Smith Woodward, F.R.S., Keeper of the Palaeontological 
Department of the British (Natural History) Museum. 
