174 THE MAMMALIA. 



resembling the Gazelles, yet almost all with horns 

 strikingly different from those of Oxen. Finally, 

 the gnu completely breaks down any systematic 

 boundary, for by the form of its hindquarters and 

 tail it resembles the horse. And into this group 

 sheep and goat have to be brought. We can, it 

 is true, distinguish them among one another by 

 the characteristic traits of the family ; for instance, 

 by the peculiar form of the skull. The ram, owing 

 to the form and solidity of the nasal, lachrymal, 

 and frontal bones, is able to give and to receive 

 those tremendous blows of forehead against fore- 

 head which would break the skull of the male 

 goat. But there are sheep with goat-like horns; 

 and an animal that is clearly a sheep from the 

 form of its skull has up to within recent times 

 been called the musk ox. 



These resemblances it may positively be as- 

 serted do not proceed from recent derivation or 

 crossings, but must be traced back except in the 

 case of the closely allied Sheep and Goats to con- 

 vergences. Moreover, the Antelopes the most 

 varied group of the living Euminants have not 

 been so carefully studied in connection with their 

 nearest fossil relatives as the Oxen. 1 



1 Kiitimeyer's valuable investigations of this group may here 

 be mentioned. 



