26 THE HORSE AND ITS RELATIVES 



be so, variation in the extent to which the depres- 

 sion is developed is exactly what would be ex- 

 pected." Mr. Pocock then goes on to observe 

 that the deeper pit observable in the skull of the 

 extinct three-toed hipparion may possibly, although 

 not probably, be also an area for muscular attach- 

 ment. He adds that in the skull of the extinct 

 South American Onohippidium, where the preorbital 

 pit (as is shown in the concluding chapter of this 

 volume) is very large, there appears to be a division 

 into two parts, of which one is shallower than 

 the other, and may correspond to the depression 

 found in some existing members of the horse 

 family. 



Apparently, therefore, Mr. Pocock is of opinion 

 that in the two extinct genera just mentioned 

 lachrymal glands were probably developed. 



A later writer, Professor Studer,^ when describ- 

 ing a species of hipparion from the upper Tertiary 

 strata of Samos, goes much further than this, and ex- 

 presses the opinion that in no case is the preorbital 

 pit for the reception of a lachrymal gland, but 

 that it is always solely for the purpose of muscular 

 attachment, and attains its maximum development 

 in species like Onohippidiuni and the Samos species 

 of Hipparion which were probably furnished with 

 a proboscis. The position of the pit, it is stated, 

 differs somewhat from that of a true larmier, and 



1 Verh. Deutsch. Zool. Ges. 1910-11, p. 11. 



