ORGANS OF SIGHT IN REPTILES. 



S39 



221 



Section of eye, 



Monitor (Varanus), 



ccxxx. 



lacrymal gland is large, especially in the Constrictors, and con- 

 tributes its secretion to that of other sources of lubrication of the 

 mouth during the long and difficult act of deglutition. 



It is interesting to note the correspondence of condition between 

 the eye and ear, in regard to the fore court of each organ, which Ser- 

 pents exclusively exemplify, among air-breathing Vertebrates. The 

 tympanic chamber parallels the conjunctive chamber; both are closed 

 externally, — the one by the ear-drum, the other by the antocular 

 membrane : the lacrymal canal is the homotype of the eustachian. 



In Lizards, fig. 221, the eyeball is less globular, more flattened 

 anteriorly than in Serpents, and the sclerotic is strengthened near 

 the cornea by a circle of small sub-imbricate osseous 

 plates, d. The lens, ib. i, is more convex behind than 

 in front ; a ' falciform process,' ib. p, is connected 

 with its capsule ; and in the Iguanas and Monitors 

 it has a delicate layer of pigment-cells. The 

 ciliary folds are more marked than in Serpents. 

 In the Geckos the pupil is vertically oval : the 

 retina shows a spot in the axis of vision. In the 

 Chameleon the cornea is small ; an antocular fold of skin is con- 

 tinued in front of the globe, but it is opake and perforated in the 

 middle : it moves Avith the eyeball ; the conjunctiva attaching it 

 to the fore-part of the ball, and the integument at its junction 

 with the skin of the head, being very thin, yielding, and wrinkled. 

 The sclerotic is so thin that the dark colour of the choroid appears 

 through it : it becomes thicker anteriorly, especially at the inser- 

 tion of the cornea. The retina shows the ' macula centralis,' or 

 * foramen Scemmerringi,' on the nasal side and a little above the 

 termination of the optic nerve, fig. 221, o. 1 The pupil is round ; 

 the lens is very small and almost spherical. The muscles have the 

 usual disposition and number ; but each eye enjoys an independent 

 motion. The great extinct marine Lizards (Ichthyosaurus) had very 

 large eyes, fig. 105, with the sclerotic plates developed even in 

 greater proportion than iii mo- 

 dern Lizards. 



In the fresh-water Tortoise 

 (Emys, fig. 222, b), the chief 

 part of the eyeball is oblately 

 spheroid, with the segment of a 

 smaller sphere at the fore-part; 

 a circle of sclerotic plates, c, 

 being imbedded at the junction, and sustaining the cornea. 



o, Lacrymal ancl Harderian elands : b, eye-ball 

 c, Sclerotic plates. Ernys Europwa. x.xxvm. 



1 cexv. pp. 1, 10-4; x\. tout. iii. p. 15C. 

 Z 2 



