THE CORNEA. 



19 



that the injection always stops at the margin of the cornea, where the tissue becomes 

 closer as it passes into the sclerotic, whereas Recklinghausen's canals are continued into 

 the cell-spaces of the sclerotic. 



Frequently in advancing- age there occurs a deposit of fatty granules at the margin of the 

 cornea, forming a whitish opaque ring about 1mm. from the corneo-sclerotic junction. This 

 ring is known as the cm ///> 



Fig. 19. VERTICAL SECTION 



OF HUMAN CORNEA FROM 

 NEAR THE MARGIN. (Wal- 



deyer.) Magnified. 



1, epithelium ; 2, anterior 

 homogeneous lamina ; 3, sub- 

 stantia propria corneoe ; 4, 

 posterior homogeneous (elastic) 

 lamina ; 5, endothelium of the 

 anterior chamber ; a, oblique 

 fibres in the anterior layer of 

 the substantia propria ; b, 

 lamellae the fibres of which 

 are cut across, pi-oducing a 

 dotted appearance ; c, corneal 

 corpuscles appearing fusiform 

 in section ; d, lamellae the 

 fibres of which are cut longi- 

 tudinally ; e, transition to the 

 sclerotic, with more distinct 

 fibrillation, and surmounted 

 by a thicker epithelium ; /, 

 small blood-vessels cut across 

 near the margin of the cornea. 



Membrane of Bow- 

 man. The part of the 

 cornea immediately be- 

 neath the anterior epi- 

 thelium, for a thickness 

 of 0*01 mm. to 0'02 mm., 

 is denser than the rest of 

 the tissue, and entirely 

 free from corpuscles (fig. 

 18, 2), (anterior homoge- 

 neous lamina, membrane 

 of Bowman). Although 

 described as a separate 

 formation it appears not 

 to differ materially in structure from the rest of the corneal substance, fibres from 

 which may be seen passing obliquely towards, and becoming lost within it 

 (fig. 19, a). It is thickest in the middle, thinning off gradually towards the edges 

 of the cornea. 



The membrane of Descemet (fig. 19, 4) (membrane of Demours, posterior 

 elastic lamina, Bowman), not very closely united with the fibrous part of the cornea, 

 is transparent and glassy in appearance. It is firm and structureless, but very 

 elastic ; and when shreds are removed from it they tend to curl up with the 

 attached surface innermost. It is not readily affected by acids, by boiling in 

 water, or by maceration in alkalies, but under some conditions it can be split up 

 into very fine lamellae. In thickness it varies from 0*006 mm. to 0'012 mm., being 

 thinnest in the middle and thickening towards the margin. Here also there are 



c 2 



