40 



THE PKJEVALSKY HOESE. 



E. 2^rjevalskii, in common with the other species of Equus, 

 possesses, in youth, an anterior (first) premolar tooth in addition to 

 the ordinary molars and premolars. This interesting tooth, in- 

 herited from the ancestors of the horse, is never replaced by a 

 permanent tooth in the modern horse. I have found it in all 

 the young skulls of the Prjevalsky horse (Nos. 5,211, 5,212, 5,215 

 and 5,214), and always in the upper jaw. In all the skulls of 

 horses, asses and onager examined, I have only once found this 

 tooth in the mandible, and then in a young ass (No. 519). 

 Nehring * states that a first premolar is not seldom present in 

 the lower jaw of the domestic horse. In ten out of fifty-seven 

 skulls examined by him he found it on both sides of the upper and 

 lower jaws. In E. i^rjevahkii the tooth is of insignificant size — 

 from 8 to 11 mm. in length, and from 5 to 9 mm. broad — pointed 

 at its apex ; placed very close in front of the next premolar ; and 

 pushed somewhat inwards. I have not found it in any skulls in 

 which the temporary teeth have been replaced by the permanent 

 dentition. 



The length of the series of cheek-teeth (Fig. 10) of E. prjevalskii 

 measured from 170 to 185 mm. in the upper jaw, and from 167 to 

 186 mm. in the lower jaw. In comparison with the other equine 

 species this length is striking ; it exceeds that of the domestic horse, 

 the donkey and the Asiatic ass ; and fails to equal that of E. grevyi 

 alone. That the conspicuous length of the series depends upon 

 the considerable dimensions of the individual teeth is shown by 

 the following- table : 



Table of Measurements of the Cheek-teeth of 

 E. Prjevalskii. 



* A. Nehring. Uelier den sog. Wolfszahn der Pferde im Hinliliek aiif die 

 genealogisehe Zu.'iammensetzung der fossilen und lebenden Equiden. — Sitsungsbr. 

 der naturforschrnden Freunde zu Berlin. No. 3 and 4. 



