the Common Horse (Equus caballus), there was an extinct species known as Steno's Horse (Equus stenonis), and distinguished by the small size of the so-called front inner pillar of the upper molar teeth' (Fig. 61). 
FIG. 61. MOLAR TOOTH
(NAT. SIZE) OF STENO'S
HORSE (E. stenonis),
with a short pillar (p).'In this respect the species in question was less specialised than the Modern Horse, and makes a step in the direction of the under-mentioned Hipparion.'[1] From these and other statements it is evident that Lydekker believed that the modern horse (Equus caballus) (Fig. 58) differed from Equus sivalensis of the Indian Pliocene, and from the extinct species Equus stenonis of the upper Pliocene and lower Pleistocene of Europe, in having long-pillared upper molars, more especially in having the 'pillar' of the last premolar longer than that of the second molar.
Hitherto molars with a short 'pillar' from Pliocene and Pleistocene deposits of Europe and North Africa have been regarded as belonging to the extinct species Equus stenonis. Further, it has been generally assumed that domestic horses are descended from a variety of Equus stenonis, which acquired long-pillared molars.
In 1907 I pointed out that one of the Newstead skulls differs from the skull of a horse of the 'forest' type (i.e. from a typical member of the species caballus) in having the face bent downwards on the cranium (Fig. 3) Pl. XCVI.), the premaxillae long and narrow, the first premolar (wolf tooth) large, and the three large premolars and the three molars smaller than in the common horse.[2]
Recently Mr. Lydekker has pointed out that some Arabs have the face bent downwards on the cranium, the premaxillae long, the first premolars large, and the anterior pillar of the upper molars unusually short.[3]
In other words, Lydekker now realises that all the modern breeds are not characterised by long-pillared molars, and says that there is a probability that Barbs, Arabs, and Thoroughbreds are descended from Equus sivalensis.
Hence, in considering the modern horses it need no longer be assumed that they are all descended from a variety of Equus stenonis characterised by long-pillared molars.
Of the skulls from Newstead with short-pillared molars and face bent downwards on the cranium, the one represented in Plate XCVI., Fig. 3, is the most characteristic. The total length of this skull is 560 mm., and the frontal index is 53.38. Though only 2 mm. shorter than the skulls of the thoroughbreds 'Orlando' and 'Bend Or,' the bent Newstead skull (if one may judge from the dimensions of the metacarpals) belonged to a horse which measured little more than 14 hands at the withers.
While the bent Newstead skull is of nearly the same length as the skull of Orlando,' it differs from 'Orlando's' skull and from the skull of the Arab
1 Lydekker, British Mammals, p. 310, 1895.
2 Ewart, Trans. Royal Soc. Edin. 1907, pp. 565–6.
3 Lydekker, Guide to the Equidae in the British Museum, pp. 19–21, 1907.
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