THE FIELD OF VISIOX 



23 



apophyses of the outer margin of the orbit are in contact, 

 and it is shut off from the temporal fossa by the orbital 

 plates of the malar and sphenoid bones, so that the orbit 



FIG. 1. Skull of a hornless sheep. (After Owen.) 



becomes a more complete bone-lined recess than in any 

 other class of mammals. In some lemurs a similar separation 

 of the orbit from the temporal fossa is met with, but in the 

 majority of them no such complete separation has taken 



(LIBRA* Y) = 



FIG. 2. Skull of a dog. 



place. The closing in of the outer wall of the orbit in Pri- 

 mates does not give prominence to the eye and enlarge the 

 monocular field as in the Ungulata, but ensures steadiness 



