370 



HITCHCOCK'S A 



N ATOMY 



Fig. 339. 



Longitudinal Section of the Globe of the Eye. 1, Sclerotic, thicker behind than in 

 front. 2, Cornea, received within Anterior Margin of Sclerotic, and connected with it by 

 means of a beveled edge. 3, Choroid, connected anteriorly with (4,) Ciliary ligament, 

 and (5,) Ciliary Processes. 6, Iris. 7. Pupil. 8, Third Layer of Eye, Retina terminating 

 anteriorly by abrupt border at commencement of Ciliary Processes. 9, Canal of Petit, 

 encircles the Lens (12); the thin layer in front of this canal is the Zonula Ciliaris, a pro- 

 longation of Vascular Layer of Retina to the Lens. 10, Anterior Chamber of Eye con- 

 taining Aqueous Humor; the lining membrane, by which the humor is secreted, is 

 represented in diagram. 11, Posterior Chamber. 12, Lens, more convex behind than 

 before, enclosed in its proper Capsule. 13, Vitreous Humor enclosed in Hyaloid Mem- 

 brane, and in cells formed in its interior by that membrane. 14, Tubular Sheath of 

 Hyaloid Membrane, which serves for the passage of the Artery of Capsule of the Lens. 

 15, Neurilemma of Optic Nerve. 16, Arteria Centralis Retime, embedded in the center. 



signifying hard, because it is a firm and stout membrane. Its 

 color is nearly white, covering the posterior four fifths of the 

 eye, it is commonly called the white of the eye, and is thickest 

 in its posterior parts. 



681. Cornea, — The external covering of the front fifth 

 part of the eye is called the Cornea, from the Latin word 

 meaning horn-like, and in two respects it bears the same rela- 

 tion to the ball of the eye, as the crystal does to the watch, 

 since it is fitted into the sclerotic by a beveled edge, as is a 

 watch-glass, and also because it is perfectly transparent. The 

 blood-vessels of this membrane are among the smallest in the 

 body, being too small to allow the passage of the blood-cor- 

 puscles, and only convey the plasma or serum. 



680. Describe the sclerotic coat. 681. What is the cornea? To what may it be com- 

 pared in the watch ? 



