152 Mammalia. Organ of Sight, 



Memhrana nictitans may he rudimentary or absent . 



In Man and the Quadrumana, at the inner Canthus, opposite the 

 puncta lachrymalia, there intervenes a vertical fold of conjunctiva, 

 the plica semilunaris, resting on the eye ball, which is a rudiment of 

 the membrana nictitans. 



The presence of this eyelid in the Sirenia distinguishes them from 

 the Cete, in which it is absent. 



12. The Lachrymal glands. 



In the Cete there are no true Lachrymal glands : but in the 

 Dolphins a ring-shaped gland behind the eyelids is present*. 



Caruncula Iqchrymalis coexists with Harderian glands in the 

 Hog tribe and the Sheep. 



Rapp. 



