OKGASS OF STGIIT IN RErXILES. 



339 



221 



Sct^Llon of eyo, 



Jlotllti.r iVarun^i, 



co.xxx. 



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

 tribntcs its secretion to that of otlicr sources of luhrication of tlie 

 mouth during the lon<r and diflSeult 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, whicli Ser- 

 pents exclusively exemplify, among air-breathing Vertebrates. Tlie 

 tympanic chamljer 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 eustacliian. 



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

 anteriorly than in Serpents, and the sclerotic is strengthened near 

 the cornea l)y a circle of small sub-imljricate osseous 

 plates, d. Tlie lens, ib. i, is more con^'ex behind than 

 in front ; a ' falciform i)rocess,' ib. p, is connected 

 with its capsule ; and in the Iguanas and IMonitors 

 it has a delicate layer of pigment-cells. The 

 ciliary folds are more marked tlian 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 with 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. 

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

 through it : it becomes thicker antei'iorly, especially at the inser- 

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

 ' foramen Samimerringi,' on the nasal side and a little above tlie 

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

 the lens is very small and almost spherical. The muscles ha'\'e the 

 usual disposition and number ; but each eye cnjoj-s an independent 

 motion. The great extinct marine Lizards {IcJitlii/osauriis) had very 

 large eyes, fig. 105, with the sclerotic plates de-^-eloped even iu 

 greater projiortion than in \i\o- 

 dern Lizards. 



In the fresh-water Tortoise 

 {Emys, fig. 222, h), tlie chief 

 part of the eyeball is oblately 

 s])heroid, with the segment of a 

 smaller sphere at the fore-part; 

 a circle of sclerotic plates, c, 

 being imbedded at tlie junction, and sustaining 



' ccxY. ]i]>. 1, 101; x\-, toni. iii. ]i. 15fi. 

 Z 2 



, T.iinymnl mid IT ml 

 :■, SdcroticrhilLs L 



lie cornea. 



