THE HOESE. 



143 



Q. How is the choroid coat connected with the 

 sclerotica? — A. By cellular membrane. 



Q. What is remarkable at its outer edge ? — A. It is 

 thrown into folds, called cUiary circle and processes. 



Q. What is the color of the choroides ? — A. Extern- 

 ally, its whole surface is black ; internally, the anterior 

 parts are black, and the jDOsterior half is of a brilliant 

 variegated green. 



Q. AVhat is the black part termed ? — A. Pigmentum 

 nigrum. 



Q. What name is given to the variegated part ? — A. 

 Tapetum lucidmn. 



Q. What difference do we observe in the pigment of 

 the choroid surfaces ? — A. The imier layer is thicker 

 and more consistent than that found on the outer 

 sm-face. 



RETINA. 



Q. What is the retina ? — A. It is the thii-d or mner- 

 most tunic of the eye. It cannot, however, be con- 

 sidered as a tunic, for it pervades the interior of the 

 globular expansion without contracting any adhesions 

 until it has reached the corpus cihare. 



Q. How is the retina fonned ? — A. The optic nerve, 

 having reached the inner and inferior part of the globe 

 of the eye, enters the sclerotic and choroid coats, and 

 in its jDassage through them its diameter contracts; 

 ha^•ing arrived at the inner part of the globe, the nerve 

 forms an eminence, from the circumference of which 

 issues radiating fibres which form the retina, 



Q. How is the retina sustained in this state of globu- 

 lar expansion ? — A. By the humors of the eye, which 

 keep it in contact ■nith the choroides. 



Q. The retina ha^g radiated on the interior of the 

 globe, where is it inserted ? — A. Lito the corpus cihare. 



HUMORS OF THE EYE. 



Q. Of how many humors does the eye consist, and 

 what are their names? — A. Of three; they are called 

 aq^ueous, crystalline, and vitreous humors. 



Q. What parts of the eye do they occupy ? — A. 

 They occupy m succession the spaces termed anterior, 

 middle, and posterior chambers of the eye. 



AQUEOUS HUMOR. 



Q. What is the use of the aqueous humor ? — A. It 

 transmits the rays of Hght, and aids the free motions of 

 the u'is. 



Q. 'What are its boundaries ? — A. It fills the interval 

 between the cornea and crystalline lens. 



Q. Describe the aqueous humor. — A. It is a bright 

 limpid fluid, and in properties bears some resemblance 

 to the \-itreous. 



Q. What is the composition of both these humors ? 

 — A. They are composed of albumen, gelatine, and 

 mm'iate of soda, held in solution by an aqueous men- 

 struum. 



Q. How is this fluid secreted? — A. By secretion from 

 the transparent walls of its capsule. 



CRYSTALLINE LENS. 



Q. "What is the use of the crystalline lens? — A. It 

 concentrates the rays of Hght, so as to make a distinct 

 image in the posterior chamber. 



Q. Where is the crystalline lens situated ? — A. Be- 

 tween the aqueous and vitreous humors. 



Q. By what is the crystalline lens enclosed? — A. 

 By a tunic, called tunica crystalluia. 



VITREOUS HUMOR. 



Q. What is the vitreous hmnor, and where is it situ- 

 ated ? — A. It is the most bulky humor of the eye ; of 

 a jelly-like consistence, yet quite transparent, and occu- 

 pies that portion of the eyeball posterior to the crystal- 

 line lens. 



Q. What is the use of the vitreous humor ? — A. It 

 supports the form of the eye, and maintains the other 

 humors in theu* proper positions. 



