374 



an inch in diameter from right to left and nine tenths of 

 an inch both in its vertical diameter and from front to 

 back. It has the appearance of having been formed by 



the union of two spheri- 

 cal segments of differ- 

 ent size. The smaller 

 segment, which forms 

 about one sixth of the 

 whole, is set upon the 

 larger and forms the 

 projecting transparent 

 portion in front. The 

 walls of the eyeballs 

 are made up of three 

 separate layers, or 

 coats an outer coat, 

 a middle coat, and an 

 inner coat (Fig. 1 59). 



FIG. 159. Diagram of the eyeball in The O uter C at sur- 

 position. i. Yellow spot. 2. Blind spot, rounds the entire globe 



3. Retina. 4. Choroid coat. 5. Sclerotic o f the eye and consists 



coat. 6. Crystalline lens. 7. Suspensory liga- Q twQ tg the 



ment. 8. Ciliary processes and ciliary muscle. 



9. Iris containing the pupil. 10. Cornea, sclerotic Coat and the 



ii. Lymph duct. 12. Conjunctiva. 13. In- cornea. The sclerotic 



ferior and superior recti muscles. 14. Optic coa f covers the greater 



nerve. 15. Elevator muscle of eyelid 16. Bone. i(m Q ^ j r 

 A. Posterior chamber containing the vitreous 



humor. B. Anterior chamber containing the spherical segment and 



aqueous humor. is recognized in front 



as " the white of the 



eye." It is composed mainly of fibrous connective tissue 

 and is dense, opaque, and tough. It preserves the form 

 of the eyeball and protects the portions within. It is 

 pierced at the back by a small opening which admits the 



