THE FROG 93 



optic capsule, save at the point where the optic nerve leaves it, and 

 here it is reflected, getting thinner to form a sheath for the nerve. 

 The exposed surface of the cornea is closely covered by skin, a con- 

 tinuation of the same skin that covers the whole body and forms the 

 eyelids, but in this region it becomes very delicate and transparent, 

 and is termed the conjunctiva. The second layer of the eyeball is 



FIG. 31. View of the human eye, divided horizontally through 

 the middle. From Furneaux. 



i, conjunctiva ; 2, cornea ; 3, sclerotic ; 4, sheath of the optic nerve ; 5, choroid ; 6, ciliary 

 processes ; 7, iris ; 8, pupil ; 9, retina ; 10, anterior limit of the retina ; n, crystalline lens ; 

 12, suspensory ligament; 13, ciliary muscle; 14, aqueous chamber; 15, vitreous chamber; 

 1 6, yellow spot ; 17, blind spot. 



known as the choroid coat, and is formed of densely pigmented con- 

 nective tissue containing blood-vessels. The choroid layer fits 

 closely on to the sclerotic over the inner parts and, like it, is partly 

 reflected over the optic nerve. At the edge of the cornea the choroid 

 coat leaves the sclerotic and becomes stretched across the eyeball, 

 so dividing it into two parts known as the anterior and posterior 

 chambers. The anterior or outer chamber is filled with a watery 



