564 
PROFESSOR OWEN ON FOSSIL REMAINS OF EQUINES 
fig. 1, p 4, n) between the outer longitudinal channels (/,/) is narrower, and is not itself 
grooved along its summit; the dentinal lobes, c, d, have less thickness or extent in the 
direction from the outer to the inner side of the tooth ; the production, o , of the lobe 
d is narrower, and the corresponding production or appendage, m, of the lobe c is 
narrower or more compressed from the outer to the inner side of the grinder ; it is 
consequently less prominent ; but it is equally expanded both anteriorly and posteriorly 
to the connecting isthmus. The folding of the enamel of the islands h and i is 
about as much as in Equus curvidens, Plate LXI. fig. 2, and in E. caballus , Plate 
LYII. fig. 1. But the most distinctive character of the upper grinders of Equus con- 
versidens is their disposition in the jaw, denoted by the nomen triviale of the extinct 
Mexican Horse ; and to the character of the curvature of the molar series of alveoli 
may be inferentially added a concomitant modification of the shape of the upper jaw 
itself, involving that of the lower one. 
The bony palate is less arched or concave from side to side in Equus conversidens 
than in any modern Equine. 
Admeasurements of part of the upper jaw and teeth of Equus conversidens , Plate LXI. 
inches, lines. 
The length of the molar series in a straight line 5 8 
„ premolars „ 3 3 
„ molars „ 2 5 
Interspace between right. and left last molars (m3) 4 0 
,, ,, first premolars (j» 2) 2 4 
Figure 3, Plate LXI. gives the grinding-surface of the third and fourth milk-teeth, 
right side, upper jaw, corresponding in size with the third and fourth premolars of Equus 
conversidens , and most probably from a young animal of that species. 
From the teeth figured by Rutimeyer* as the deciduous molars of the Equus fossilis 
those of Equus conversidens differ in the greater degree of compression of the crown from 
without inwards, in the minor indication of the indent j, and simpler character of the 
fold g (marking off the postinternal lobule), in the less prominence and in the flattening 
of the ridge n (dividing the channels/,/'), and in the minor thickness and prominence 
of the lobule m. 
From the milk-molars oi Equus caballus (Plate LVII. fig. 3, d 3, d 4) they differ also 
in the greater fore-and-aft extent and flattening of the external longitudinal ridge, n, 
in the minor relative breadth from without inwards, in the greater proportion of the 
part of the crown behind the lobule m, and in the more generally plicated disposition 
of the enamel. 
The proportions of the crown of the permanent upper molars of Equus fossilis (from 
Kent’s Hole, ‘ British Fossil Mammals,’ p. 383, fig. 143) are well brought out in com- 
parison with the immature teeth of Equus fossilis figured by Rutimeyer {loc. cit.) ; it is 
* Beitrage zur Kentniss der Fossilen Pferde, 8vo, 1863, Taf. I. fig. 12. 
