I 



THE ORGANS OF SPECIAL SENSE 



which it is separated by a thin membrane; it is invested 

 by a transparent elastic membrane, called the capsule of 

 the lens. The lens consists of concentric layers arranged 

 like the coats of an onion. The external layer is soft, and 

 each successive one increases in firmness until the central 

 layer forms a hardened nucleus. These layers are best 

 demonstrated by boiling or by immersing in alcohol, 

 when they easily separate from one another. 



FIG. 135. Crystalline lens and suspensory ligament or zonula: i, Lens; 

 2, posterior, and 3, anterior portion of zonula ; 4, its insertion into the pre- 

 equatorial region. The black rays are lines of pigment torn from the ciliary 

 processes, and belong in reality to the ciliary portion of the retina (Testut). 



The vitreous humor forms the principal bulk of the 

 globe of the eye. It is an albuminous fluid, resembling 

 the aqueous humor, but is denser, and differs from the 

 aqueous in this important particular, that it has not the 

 power of reproducing itself. If, therefore, by accident it 

 is discharged, the eye is irrecoverably lost; whereas, if the 

 aqueous humor is discharged, it will again be restored. 

 The vitreous is enclosed in a delicate membrane, called the 

 hyaloid, which sends processes into the interior of the globe 

 of the eye, forming the cells in which the humor is retained. 



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