2 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 60 



Equus caballus, but it stands at the extreme as regards length and 

 narrowness, the horse being intermediate in shape of skull between 

 this type and the asses and zebras. Four skulls of Equus caballus 

 prseevalskii in the British Museum have been used for making these 

 comparisons, as they represent best the original wild horse type. 

 These four skulls are shorter and broader than that of the normal 

 domestic horse and resemble the skulls of wild asses more closely. 

 Skulls of the domestic breeds of horses vary considerably in length 

 and narrowness, but none are as dolichocephalic as Dolichohippus, 

 and all differ from this genus in the shorter rectangular shape of 

 the facial portion of the lachrymal bone. In fact, Dolichohippus 

 grevyi is the only species of the old genus Equus which shows 

 appreciable distinctive skull characters. It is more widely separated 

 from true Equus than this is from Asinus or Hippotigris. The two 

 latter genera show no skull characters which will separate them. 

 Hippotigris represents the extreme as regards shortness of skull, 

 roundness of interorbital region, and small size of lachrymal bone ; 

 Asinus is somewhat more dolichocephalic and flatter in the inter- 

 orbital region, "while Equus is often quite dolichocephalic anteriorly, 

 but lacks any occipital elongation. 



The three equine genera Equus, Asinus and Hippotigris differ 

 collectively from Dolichohippus by their shorter and broader skulls, 

 shorter and more rectangular lachrymal bone (the depth of which 

 nearly equals its length from the orbital rim), the position of the 

 lateral nasal notch (which is at the suture of the nasals and pre- 

 maxillse), and the shorter lambdoidal crest (which terminates ver- 

 tical in respect to the auditory meatus). Hippotigris differs further 

 in having a rounded or convex interorbital region, and shorter pos- 

 terior extension of the facial portion of the lachrymal bone which 

 does not extend beyond the nasal bones. Other differences in that 

 genus are the small ears, broad stripes, narrower hoofs and larger 

 ergots on forelegs. The mountain zebra, H. zebra, shows only slight 

 skull differences from the quaggas or burchelli group, although the 

 wide color differences and diverse habits would lead one to anticipate 

 other structural peculiarities in this form. The shape of the ear of 

 Dolichohippus is quite different in its greater breadth from that of 

 Asinus, in which genus the ears though equally long are narrow. 

 The hoof, though strikingly different from that of Hippotigris and 

 the narrow-hoofed species of Asinus in its large size and breadth, is 

 very similar in these two characters to that of the kiang, Asinus 

 kiang. 



