PROTECTIVE MECHANISMS OF THE EYEBALL 105 



of a herd may be guided to rejoin its fellows. They seem 

 also to have some connection with the sexual function, as 

 they are usually larger in the male than in the female, and 

 their growth is said to be arrested by castration. In arboreal 



M 



Fia. 25. — Lining membrane of the suborbital pit of a sheep. 



mammals, like monkeys and anthropoid apes, the sense of 

 smell is of but little use; the olfactory organs are com- 

 paratively poorly developed, and the odoriferous organs 

 at the inner angles of eyes have dwindled into vestigial 



