20 THE HORSE FAMILY. 



Mongolian Wild Horse, in which the length of the tooth-row 

 is 7^ inches. The upper cheek-teeth (fig. 16, C) in the skull of 

 an Arab presented by Mr. Wilfrid Scawen Blunt (N.H. 20) and 

 likewise remarkable for the extensive folding, or frilling, of the 

 enamel in the centre of the crown ; while in both the Arab skulls 

 in the collection the anterior pillar of the upper molars presents 

 an unusually short grinding surface. Both these features are 

 noticeable in the cheek-teeth of the extinct Equus sivalensis of 

 India ; the skull of that species (N. H. 42) likewise displaying a 

 vestige of the preorbital depression in a more marked degree than 

 in Arabs and Thoroughbreds. In all these respects the skulls 

 of Arabs and Equus sivalensis approximate to that of Hijiparioyi 

 (N.H. 49). 



The skulls of Arabs (fig. 18) difi:er markedly from those of ordi- 

 nary Horses in the strongly sinuous profile of the face, in the narrow 

 muzzle, and in the great width and depth of the hinder part or 

 ^^ angle ^^ of the lower jaw^, as well as in certain minor details; all 

 these features corresponding with the contour of the head of living- 

 Arabs. Some Thoroughbreds, such as those of the ^' King Tom " 

 line, exhibit the characteristic Arab profile very distinctly. 



Among Mr. Blunt^s Arab stud the presence of a large " wolf- 

 tooth," or rudimentary first premolar is stated to be far from 

 uncommon, at least in the upper jaw, whereas such large teeth 

 are rare in ordinary Horses. Such a tooth was generally, if not 

 invariably, present in both jaws in the extinct Equus sivalensis 

 and its allies. 



In addition to the features already noticed, Arabs are charac- 

 terised by the following peculiarities : — 



The skull is relatively short, very wide between tlie eye-sockets, 

 which are high and prominent, thus giving a wide field of vision ; 

 while the lower jaw is slender in front, and very deep and wide- 

 set behind. The chest is rounded, and the back and loins are 

 well " ribbed up,'' due to the presence of only five (in place of 

 six) lumbar or ribless vertebrae. The pelvis — in connection with 

 great speed — is set more nearly horizontal than in other Horses ; 

 the croup, or tail-region, is relatively high ; and there are only 

 sixteen (in })lace of eighteen) caudal, or tail, vertebrae. In the 



