BRUNIQUEL, AND ITS ORGANIC CONTENTS. 
549 
the thinness of the enamel-folds which characterize the Equus plicidens from Oreston * 
and from Newborne, North Carolina j\ 
The inner enamel-folds of the upper grinders of var. B of Equus spelceus are more 
wavy than those in var. A ; but if the first upper grinder, p 2, of Equus spelceus, var. B 
(Plate LX. fig. 3), be compared with that tooth of Equus plicidens (‘ British Fossil 
Mammals,’ p. 392, fig. 152), it will be seen that, besides the thicker and less plicate 
enamel of E. spelceus , the crown is longer, and more acute anteriorly, in the Bruniquel 
Equine. The differences presented by the fossil Equines of America will be noticed in 
a subsequent paper ; those which are seen in the Asiatic and European Miocene Horses 
{Hipparion, Cut, fig. 3) are still more decisive. 
Amongst the less complete specimens of Equine jaws and teeth from the Cave of 
Bruniquel a few were found which illustrated phases of dentition, and lend further 
help in tracing out the affinities of the species. The subject of Plate LX. fig. 4 is the 
grinding surface of the last four molars, left side, upper jaw, of a young animal, with 
the first and second true molars, ml, m2, abraded by mastication, and with the last 
premolar, p 4, and last molar, m 3, not yet in place. This phase of dentition is almost 
identical with that shown by the Zebra (Plate LX. fig. 1). But there the summits of 
the inner lobes of p 4 have began to show attrition ; whilst in the Cave-Equine the 
antero-internal lobe of m 3 has just been touched, and no part of p 4 shows any action 
of the opposing tooth. Occasionally, in Equus caballus, the last molar a little precedes 
the last premolar in coming into action. At the phase of development shown in Plate 
LX. figs. 1 & 4, the analogy of the immature grinder, p 4, to the fully developed one in 
the paleontologically earlier Equine ( Hipparion ) is interestingly exemplified. The inner 
lobule, m, is a column detached at the summit, which when abraded, as in Plate LX. 
fig. 1, p 4, shows an island of dentine girt by enamel, as in the corresponding, but older 
and more worn, tooth of Hipparion. The earlier confluence of the column with the 
body of the tooth in Equus, occasions the earlier conversion in the course of attrition 
of the island into a peninsula, as in m 1 & m 2 of figs. 1 & 4. The' later confluence of 
the column, or the maintenance of its distinctness nearer to the base, occasions the 
longer retention of the insular figure of m in the upper molars of Hipparion ; but 
in old or much-worn grinders of this genus it also shows continuity of dentine with 
the lobe c. 
The young Equus spelceus differs from the young Zebra in the greater relative size of 
the column m, leading to the corresponding greater antero-posterior and transverse 
diameters of the lobe m when worn into union with the rest of the tooth, as in Plate 
LX. fig. 3 ,p 4. 
The nearer affinity to Equus caballus is likewise shown by the larger size of the first 
and second molars ( m 1, m 2, fig. 4). But the last molar retains, in the present young 
* Brit. Boss. Mam. p. 392, figs. 152, 153. 
f Leidy, Proc. Amer. Acad, of Sci. Philadelphia, September, 1847, p. 262. 
MDCCCLXIX. 4 E 
