292 



THE SPECIAL SENSES 



tunics. The former are the aqueous humor, Fig. 64, A, the 

 crystalline lens L, and the vitreous humor v. Of these the lens 

 alone is solid. The three coats of the eyeball are called the 

 sclerotic s, the choroid Ch, and the retina R. This arrangement 

 exists in respect to five-sixths of the globe of the eye, but in 

 the anterior one-sixth, these coats are replaced by the cornea c, 

 which is thin and transparent, so that the rays of light pass 

 freely through it, as through a clear window-pane. 



61. In shape, the cornea is circular and prominent, resem- 

 bling a miniature watch-glass, about -^ of an inch thick. In 



FIG. 64. VERTICAL SECTION OF THE EYE (Enlarged ) 



C, The Cornea 



A, The Aqueous Humor 

 I, The Iris 



P, The Pupil 



L, The Crystalline Lens 



H, The Ligament of the Lens 



B, The Ciliary Process 



V, The Cavity containing the Vitreous Humor 

 S, The Sclerotic 



Ch, The Choroid 



B, The Retina 



N, The Optic Nerve 



DD, The Eyelids 



X, The Levator Muscle of the 



Lid 

 Y, The Upper Straight Muscle of the 



Eye 

 Z, The Lower Straight Muscle 



Upper 



structure, it resembles horn (as the name signifies), or the nail 

 of the finger, and is destitute 'of blood-vessels. The sclerotic 



61. The shape of the cornea ? Its structure ? The " white of the eye " ? 



