CH. LVIII.] THE EYEBALL 811 



one in each lower lid, into the lacrimal sac, and thence along the nasal 

 duct into the inferior meatus of the nose. The excessive secretion 

 poured out under the influence of an irritating vapour or painful 

 emotion overflows the lower lid in the form of tears. The secretory 

 nerves are contained in the lacrimal and subcutaneous malar branches 

 of the fifth nerve, and in the cervical sympathetic. 



The Eyeball. 



The eyeball (fig. 507) consists of the following structures : 



Sclerotic coat. 



Choroid coat. 



________________________ _ Retina. 



Ciliary muscle 



Cornea 

 Anterior chamber- 



Lens 



Iris- 



Ciliary process- 

 Ciliary muscle 



Fio. 507. Section of the anterior four-fifths of the eyeball. 



The sclerotic, or outermost coat, is made of connective tissue and 

 envelops about five-sixths of the eyeball : continuous with it, in front, 

 and occupying the remaining sixth, is the transparent cornea (fig. 508). 

 Immediately within the sclerotic is the choroid coat, and within the 

 choroid is the retina. The interior of the eyeball is filled by 

 the aqueous and vitreous humours and the crystalline lens ; but, also, 

 there is suspended in the interior a contractile and perforated cur- 

 tain, the iris, which is continuous with the choroid; it regulates 

 the admission of light; at the junction of the sclerotic and cornea is 

 the ciliary muscle, the function of which is to adapt the eye for seeing 

 objects at various distances. 



The Choroid Coat is the vascular coat of the eyeball, and its 

 connective tissue contains abundance of branched pigment cells. It 

 is separated from the retina by a fine elastic membrane (membrane of 

 Bruch). 



