ORGANS OF SIGHT IX RErTILES. 



341 



22G 



.1 hlacker pigment, than in otlier Reptiles, and the ciliary plica; are 



longer and more distinct, extending beyond the origin of the iris. 



Tins is anteriorly of a pale yellow colour ; the pupil is vertical. 

 The eye of the Crocodile is chiefly peculiar for the massive and 



complex character of its appendages, fig. 22G, to whicii the eye- 

 ball itself, x, u, t, bears but a small 



proportion. No other or higher 



animal ofters such a structure : it 



was one of the discoveries of 



Hunter, who left a drawing of it, 



which was engraved, and, with his 



preparation, no. 1770, described in 



XX. vol. iii. In the copy of this 



drawing, fig. 226, the upper, e, and 



lower, h, eyelids are severed at the 



outer canthus, and drawn apart to 



show the third or nictitant eyelid, //, 



and the extent of the conjunctiva. Of 



this membrane e is the free surfiice of 



the part which lines the ordinary 



eyelids, whence it is reflected over 



the nictitant lid at ij, li, k ; and then 



upon the cornea at the line maidvcd e' , u]>on the part of the 



circumference next the outer canthus. The free margins of 



the upper and lower lids are marked c ; they arc devoid of cilia, as 



in all Ilcematocrya : h is the free margin of the third lid. The 

 glands sending their secretion to the conjinictival space are the 

 proper lacrymal and the harderian ; the duct of the latter termi- 

 nates on the inner surface of the base of the nictitant lid, at /■. 

 From the conjunctival chamber the secretion of both glands is 

 conveyed by the two puncta lacrymalia, f, to the duct termin- 

 ating in the nasal cavity. The muscles are divisible into those of 

 the eyelids and those of the eyeball. The nictitator, fig. 226, z, 

 arises from the inner and upper part of the ball, proceeds outward 

 and downward, winding round the optic nerve and choanoid muscle 

 (which protects the nerve from the pressure of the nictitator in 

 action), and is inserted into the inferior angle of the third lid. 

 "Whilst the muscle draws this outward over the eyeball, it at the 

 same time rotates the ball inward beneath the third lid, being 

 attached to movable points at both extremities. The upper eyelid 

 has a levator muscle, m, chiefly inserted into the palpebral ossicle, 

 but also sending a few fibres, n, to be attached to the paliiebral 

 conjunctiva near its angle of reflection. The under lid has a 



