THE EYE. 



333 



In life these fixed bodies nearly fill the lymph-spaces and 

 conform to their size and shape ; they are flat corpuscles, usu- 

 ally nucleated, and have short, sharp-pointed processes, which 

 pass out into the minute lymph-canals. In the lymph-spaces 

 of the cornea are also found, even in normal conditions, a few 

 migratory cells, resembling white blood-corpuscles ; they are 

 very numerous when the cornea has been irritated, and can 

 be seen in a frog's cornea, which 

 has been kept five to fifteen 

 minutes in serum or aqueous 

 humor in a moist chamber, and 

 examined without pressure on 

 a warm slide. 



Beneath the substantia pro- 

 pria of the cornea we find the 

 posterior limiting layer, or 

 Descemet's membrane (cT) (Fig. 

 151). This is transparent, ap- 

 parently homogeneous, rolls up 

 when cut, is intimately connect- 

 ed with the posterior fibres of 

 the cornea proper, and is lined 

 on its inner surface with endo- 

 thelium (e). It contains no cel- 

 lular bodies, but, like the anterior limiting layer, can be sepa- 

 rated into fibrillae, and appears to represent a concentration of 

 the corneal fibres rather than a separate structure. 



The endothelium is a single layer of flat cells lining the 

 anterior chamber. Blood-vessels are found only in the normal 

 cornea at the periphery, where they form a fine network con- 

 necting with the conjunct! val and scleral vessels. 



The 'nerves enter the cornea at the posterior part of the 

 periphery ; they soon lose their neurilemma and medullary 

 sheath, and pass forward obliquely, as small axis-cylinders, 

 toward the epithelial layer ; here they divide up into branch- 

 lets, often having a ganglionic enlargement at the point of divi- 

 sion. Under the epithelium these delicate fibres form a net- 

 work which sends some very minute filaments upward between 

 the epithelial cells. Their further course is unknown. 



To separate the cornea into its constituent fibres, small pieces 

 should be soaked for twenty-four hours in a concentrated pi- 



FIG. 152. Lymph spaces and canals, A ; fixed 

 corneal cell, partly filling these spaces, B. After 

 Waldeyer. 



