264 



OF THE PRIMARY TISSUES OP THE HUMAN BODY. 



ture. The interspaces left between the superposed layers have the form of tubes, 

 arranged with tolerable regularity, and constricted at intervals (Fig. 56); these 



Fig. 56. 



Fig. 57. 



- Hil 



l 





Tubes of the Cornea Proper, as shown in the eye of the Ox by mercurial injection. Slightly magnified. 



are more readily demonstrated, however, in the corneae of large quadrupeds than 

 in that of man. This lamellated tissue is the only part of the cornea, which is 

 continuous with the sclerotica ; and its fibres appear to be very similar, in every 

 respect save their extreme transparency, to those of that tissue. The anterior 

 elastic lamina is a very thin stratum of homogeneous membrane, not affected by 

 maceration, boiling, or acids, which intervenes between the epithelial layer and 



the lamellated tissue ; apparently serving as a 

 "basement membrane" to the former; whilst it 

 is tied down to the latter by filaments of elastic 

 tissue, which pass from its internal surface to 

 lose themselves among the superficial lamellae. 

 This layer disappears at the margin of the cor- 

 nea, expending itself apparently in giving origin 

 to an increased number of these filaments, some 

 of which pass into the sclerotic coat. The pos- 

 terior elastic lamina (or "membrane of De- 

 mours" or "of Descemet") resembles the ante- 

 rior in the characters of its texture; but its ad- 

 hesion to the posterior surface of the lamellated 

 cornea is comparatively slight, no filaments 

 being sent down from it among the lamellae . No 

 vessels can be traced into the substance of the 

 Cornea ; but its margin (like that of an articu- 

 lar cartilage) is surrounded by a vascular circle, 

 which consists of two sets of vessels, a super- 

 ficial and a deep-seated (Fig. 57). The arteries 

 of the former, according to Mr. Toynbee, 1 are 

 derived from the conjunctiva! membrane, and 

 are prolonged for a short distance upon the outer 

 layer of the cornea ; but they terminate in veins 

 at from |th to a line from its margin. The deep- 

 seated vessels are derived from the Sclerotic; and they terminate in veins just 

 where its tissue becomes continuous with that of the Cornea. In diseased con- 

 ditions of the Cornea (as of the articular cartilages), both sets of vessels extend 

 themselves through it; the superficial not unfrequently form a dark band of 

 considerable breadth round its margin ; whilst the deep-seated are prolonged into 

 its entire substance. Notwithstanding the absence of vessels in the healthy 



Nutrient Vessels of the Cornea: A, 

 superficial vessels belonging to the Con- 

 junctival membrane, and continued over 

 the margin of the Cornea; B, vessels of 

 the Sclerotic, returning at the margin of 

 the Cornea. 



Philosophical Transactions," 1841. 



