ZOOLOGICAL POSITION AND STRUCTURE 21 



a sheep, its possession of nipping incisor teeth in 

 both upper and lower jaws enabling it to graze 

 closer than the former, in which the upper incisors 

 are absent, although its larger muzzle prevents it 

 from equalling the latter in the closeness of its bite. 



Here also it may be mentioned that the skulls 

 of tame sheep differ from those of their wild rela- 

 tives — when specimens with the same approximate 

 basal length are compared together — by the smaller 

 diameter of the socket of the eye, the abortion of 

 the auditory bulla at the base of the skull, and the 

 much smaller capacity of the brain-chamber. It 

 has been shown, for instance,^ that whereas in the 

 wild mouflon the brain-capacity ranges from 130 to 

 170 cubic centimetres, with a mean of 140 cubic 

 centimetres, in domesticated sheep skulls of the 

 same average size the mean brain-capacity is only 

 from no to 120 cubic centimetres. These differ- 

 ences are due, of course, to the more or less protected 

 conditions under which domesticated sheep pass 

 their existence, thereby reducing the need of acute- 

 ness in the senses of hearing, sight, and smell. 



The skulls of horned sheep differ from those of 

 the more typical kinds of cattle by the more for- 

 ward position of the bases of the cores of the horns 

 on the frontal bones ; but there is a minor differ- 

 ence in this respect in the case of bison and 

 buffaloes. 



' See Klatt, Sitzber. Ges. natfor. Freunde, Berlin, 1912, p. 153. 



