340 



NORMAL HISTOLOGY. 



The anterior limiting membrane, or Bowman's membrane, is 

 situated immediately below the epithelium and appears as a homogeneous 

 band, about 20 /* in thickness at the centre and thinner at the periphery, 

 where it terminates without extending into the conjunctiva of the sclera. 

 The membrane may be resolved into fine fibrillae by suitable reagents, is 

 connected firmly with the cornea proper, and is to be considered a special 

 condensation of the latter. It contains no elastic tissue. 



The substantia propria constitutes the main portion of the cornea 

 and is made up of interlacing bundles of fibrous connective tissue, directly 

 continuous with those of the adjacent sclera. The bundles are composed of 

 fine fibrillae, have a flattened form, and are so disposed as to produce regular 

 lamellae, about sixty in number, running parallel with the surface. The 

 alternating lamellae have a direction approximately at right angles to each 

 other and are frequently joined together by strands, they?r^ arcuata, which 



are especially numerous 

 in the anterior lamellae. 

 The fibrillae and bundles 

 are held together by an 

 interfibrillar ' cement-sub- 

 stance, in which are em- 

 bedded the cellular ele- 

 ments, the corneal corpus- 

 cles. These are flattened 

 connective tissue cells, 

 with faintly granular cyto- 

 plasm, . whose nuclei are 

 irregular and show nu- 

 cleoli. The cells are 

 provided with branching 

 processes which anasto- 

 mose with those of other 

 cells, both on the same 

 and adjacent levels, and 

 so constitute a continuous 

 network of protoplasm, 

 upon which the nutrition 

 of the cornea largely depends. They occupy a system of intercommunicat- 

 ing lymph-clefts, the corneal spaces, which during life they fill completely. 

 Occasional leucocytes or wandering cells are found between the fibrous 

 bundles. 



The posterior limiting membrane, also known as Descemet' s mem- 

 brane, the membrane of Demours, or the posterior elastic membrane, is a 

 homogeneous band, which varies in thickness from 6 ju. at the centre to 12 A* 

 at the periphery. It is less firmly united to the substantia propria than is 

 the anterior limiting membrane, and is less easily affected by acids, alkalies, 

 boiling water and other reagents. It resembles elastic tissue and is very firm 

 and resistent to injury or perforation from inflammation. At the periphery 

 the membrane splits up into bundles of fine fibres, which are gradually 

 strengthened into a series of firm connective tissue trabeculae. Some of 

 these form the point of attachment of the ciliary muscle; others run into the 

 iris, and still others constitute the inner wall of a circularly disposed venous 

 channel, the sinus circnlaris iridis, or canal of Schlemm. These fibres are 

 known as the ligamentum pectinatum iridis and mark the lateral limit of the 



FIG. 386. Thin sheet of corneal tissue stained to show the corneal 

 corpuscles ; surface view. X 350. 



