SECT. 224.] THE CORNEA. 539 



I. of the conjunctival membrane (conjunctiva cornea) ; 2. of the 

 proper cornea; and 3. of the membrane of Descemet: the first and 

 the last of these layers are formed by an epithelium and a sub- 

 jacent structureless membrane; the middle one of a fibrous tissue 

 of a peculiar kind. 



The proper cornea, or the fibrous layer of it, constitutes by far 

 the thickest part of the whole coat, and consists of a fibrous sub- 

 stance nearly allied to connective tissue, but yielding, according to 

 J. Mailer, chondrin instead of gelatin on boiling. This chondrin, 

 however, is stated by His to differ from the ordinary kind, in the 

 circumstance that most of its precipitates are soluble in an excess 

 of the precipitating re-agent. Its elements are pale bundles, 

 0*002'" to croo4"' in diameter, on which, at least when teased out, 

 fine fibrils are more or less distinctly visible. These, again, are 

 united to form flat bundles, of 004'" to 0-12'" in breadth (His), 

 which keep their surfaces always parallel to the surfaces of the 

 cornea, and are connected with each other, both in the direction 

 of the surface and in that of the thickness, so that they represent 

 a large mesh work extending through the entire tunic. There are, 

 however, no visible spaces in the membrane, seeing that, on the 

 one hand, the elements of one fibrous fasciculus press closely into 

 the intervals of another, and that, on the other hand, all the fibrous 

 bundles themselves lie very compactly one upon another, as in a 

 compressed sponge, for example. The structure of the cornea 

 may be most correctly and easily understood, if we proceed from 

 the sclerotic, of which the corneal tissue is only a modification. 

 We have seen that in the sclerotica, bundles of connective tissue, 

 arranged in longitudinal and transverse networks, constitute the 

 whole tunic; and the same is the structure of the cornea, only 

 more complicated, the bundles here running in the most diverse 

 directions. — If we regard the structure of the cornea as a whole, 

 we may ascribe to the tunic a lamellated arrangement, although 

 we cannot agree with many authors, in stating that it consists of 

 complete lamellae. This arrangement results from all its bundles 

 being fiat, and lying with their surfaces parallel to the surface of 

 the cornea, so that this structure cannot, without extreme difficulty, 

 be torn and penetrated in the direction of its thickness. — The 

 correspondence of the elements of the cornea with connective tissue 

 is also proved by the following considerations: 1. that it is con- 

 tinued at its borders (chiefly by its radiating elements), directly 

 and without interruption, into the similarly disposed fibres of the 

 sclerotic, so that a natural separation of the two tunics cannot be 



