559 



CHAP. XXVI. 



SIGHT. 



"THE instruments of vision, the eyes a , are 'two moveable 

 globes, fixed to the optic nerves, whose decussation we formerly 

 noticed, as it were to stalks, in such a manner that their insertion 

 is not exactly opposite the centre of the cornea and iris, but on 

 one side of this imaginary axis, rather nearer to the nose. 



" They consist of various coats containing pellucid humours 

 of different densities, so placed that the rays of light can pass 

 from the transparent anterior segment of the bulb to the opposite 

 part of the fundus. 



" The external coat is called sclerotic. It is deficient in the 

 centre, and that part is filled up by the cornea, which is trans- 

 parent, lamellated (lined internally by the membrane of the aqueous 

 humour, or of Demours), more or less convex, and projects like 

 the segment of a small globe from one of rather larger size. b 



" The interior of the sclerotic is lined by the c/iorioid, which 

 abounds in blood-vessels 6 , especially vorticose veins, and is 

 covered on each side by a black pigment, which adheres but 

 loosely to its concave surface in the form of mucus. d 



a " Sam. Th. Sommerring (the father), Icones ocuti humani. Francof. 1801. 

 fol. 



Detm. W. Sommerring (the son), De oculorum sectione horizontali Comment, 

 arius. Getting. 1818. fol." 



b " G. H. Gerson, De forma cornea deque singutari visus phcenomeno. 

 Getting. 1810. 4to. 



Al. Clemens, Tunica corneas et humoris aquei monographia. Getting. 

 1816. 4to. - 



M. J. Chelius, Ueber die durchsichtige Hornhaut. Carlsr. 1818. 8vo." 



c " Sam. Th. Von Sommerring, in the Denkschr. der Akad. der Wi$s. zu 

 Munchen. 1817. tab. 1." 



d " C. Mundini, in the Comm. Instit. JSononiens, t. vii. p. 29. 



H. F. Elsaesser (praes. G. C. Ch. Stoirr), De pigmento oculi nigro. Tubing. 

 1800. 8vo." 



P P 



