CH. LVL] 



THE EYEBALLS 



765 



one in each 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. 561) consists of the following structures : 



Sclerotic coat. 

 -Choroid coat. 

 Retina. 



Ciliary muscle- 

 Ciliary process- 

 Canal of Petit- 

 Cornea 

 Anterior chamber- 



Lens 



Iris- 

 Ciliary process- 

 Ciliary muscle- 



Vitreous humour. 



FIG. 561. Section of the anterior four-fifths of the eyeball. 



The sclerotic, or outermost coat, envelops about five-sixths of the 

 eyeball : continuous with it, in front, and occupying the remaining 



FIG. 562. Vertical section of rabbit's cornea, a, Anterior epithelium, showing the different shapes of 

 the cells at various depths from the free surface ; &, portion of the substance of cornea. (Klein.) 



sixth, is the cornea. Immediately within the sclerotic is the choroid 

 coat, and within the choroid is the retina. The interior of the 



