Organ of Sight, 149 



and most movable, and rarely has a proper * depressor' muscle, 

 but falls down by its own elasticity on the relaxation of the 

 * orbicularis ' which draws it up. The upper eyelid is occa- 

 sionally provided with cilia. The third, innermost, eyelid is 

 vertical, and termed the membrana nictitans, it contains 

 muscular fibres, and extends over the eye when that is drawn 

 back by the action of the * suspensorious' muscle ; it is some- 

 times small, rudimentary, or absent. 



The Lachrymal Glands are often small, and sometimes ap- 

 pear to be wanting. A special gland, subserving the move- 

 ments of the third or nictitating eyelid, termed the Harderian 

 gland, is present in all quadrupeds up to the Quadrumana, 

 though occasionally represented merely by an aggregate of 

 follicles, somewhat more complex than the 'Meibomian,' at 

 the inner side of the eyeball*. The group of glandular fol- 

 licles sometimes found occupying the recess of the inner 

 canthus, and named the * Caruncula Lachrymalis,' are gener- 

 ally absent when the Membrana Nictitans is much developed, 

 and therefore seldom coexist with the Harderian gland. In 

 all Mammals with divided or horizontal eyelids there is found 

 a provision for carrying ofi" the waste lubricating fluid of the 

 ej^eball, similar to that in Man. 



Special. 



1. Uye. 



Rudimentary y &c. 



In certain burrowing Insectivora, and Rodentia, e.g. Chrysoehloris 

 and Talpa caeca (Insectivora); Spalax typhlus (mole rat), Mus typhlus 

 (Rodentia). 



Situated laterally with prominent Cornea. 



e.g. in JerloidcB and Leporidce (Rodentia) ; and Horse (Pcrissodac- 

 tyla, Solidungula). 



in Ruminantia (Artiodactyla) the eyes are lateral. 



e.g. in Cete and Proboscidia. 



