536 
PROFESSOR OWEN’S DESCRIPTION OE THE CAVERN OE 
Upper Molars. — Cuvier, with his usual acumen, had detected beneath a general 
resemblance to the ruminant pattern in the Horse’s grinders the more essential corre- 
spondence with that of the (perissodactyle) section of Ungulates to which the genus is 
essentially allied*. I here contrast an upper molar (mV) of Paleeotherium (fig. 1), of 
Paloplotherium (fig. 2), and of IHpparion (fig. 3) with that of Equusf, fig. 4. 
Fig. 3. 
Fig. 4. 
Upper molar, Hipparion. 
Section of upper molar. 
Horse ( Equus cabaTlus). 
The longitudinal tract of dentine extending along the outer side of the crown (‘ colline 
longitudinale externe,’ Cuv.) is partially divided by the two indents, f, f, into an ante- 
rior, a, and posterior, b, lobe: the tract of dentine along the inner side of the crown 
is divided by an oblique fold or valley, e, into two lobes, c, d, extending obliquely 
backward from the outer tract, a, b, toward the inner side of the crown ; these are the 
‘ deux collines transversales ’ of Cuvier. Besides the fold, e, there is a shorter pos- 
terior one, g. These oblique folds or valleys are of more even depth in Paleeotherium 
(fig. 1) than in Rhinoceros and Equus (fig. 4) ; they are so shallow, midway, in the latter, 
as to lead to an early separation of their respective beginnings or entries, g and e, from 
their terminations, h and i : the anterior oblique lobe, cm, is separated by the valley, e h, 
from the posterior oblique lobe d o ; which is defined by the valley, g i, entering from 
the posterior side of the crown. The blind terminations of the two valleys, h and are 
more dilated, and their enamel-margin is more wavy, in Hipparion (fig. 3) and in Equus 
(fig. 4) than in Paleeotherium , fig. 1 ; and, being soon cut off from the rest of the valley, 
in the wear of the equine tooth, they form the irregular crescentic islands, h . i, in figs. 3 
& 4, leaving the entries of the valleys as shallow or short indents, g , e. The grinding- 
surface of the horse’s tooth is made further complex by an indent, k, near the anterior 
internal angle, which, being nearly met by a fold of the main valley e, defines the acces- 
* “ Les dents mach.eli.eres superieures de chevaux sont prismatiques comme celle de boeuf et de buffle, et 
marquees de meme de quatre croissans.”. . Au reste cette forme de couronne, tout en se rapprochant des rumi- 
uans, ne s’eloigne pas autant du rhinoceros qu’on pourrait le croire : elle peut aussi se reduire a une colline 
longitudinale externe et a deux collines transversales, qui envoient chacune un crochet en arriere .” — Recherches 
sur les Ossemens Fossiles, Ed. 8vo, 1834, t. iii. pp. 202, 203. 
f This comparison is given and illustrated in my ‘ British Fossil Mammalia,’ 8vo, 1846, p. 384, figs. 126 
& 143, and in Art. “Odontology,” Encycl. Britan, vol. xvi. 1858. See also Rutimeyee, * Beitrage zur Kenntniss 
der fossilen Pferde,’ 8vo, 1863, tab. i. 
