CORNEA, AND CRYSTALLINE LENS. 159 



densely interlaced in various directions, and mingled with elastic fibrous tissue, flatten out 

 into a membranous form, so as to follow in the main the curvatures of the surfaces of the 

 cornea, and to constitute a series of more than sixty lamellae, intimately united to one ano- 

 ther by very numerous processes of similar structure, passing from one to the other, and 

 making it impossible to trace any one lamella over even a small portion of the cornea. The 

 resulting areolaj, which in the sclerotic are irregular, and on all sides open, are converted in 

 the cornea into tubular spaces, which have a very singular arrangement, hitherto undescribed. 

 They lie in superposed planes, the contiguous ones of the same plane being for the most part 

 parallel, but crossing those of the neighbouring planes at an angle, and seldom communica- 

 ting with them (fig. 58). The arrangement and size of these tubes can be shown by 



Fig. 58. 



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



driving mercury, or coloured size, or air, into a small puncture made in the cornea. They 

 may also be shown under a high power by moistening a thin section of a dried cornea, and 

 opening it out by needles. The tissue forming the parietes of these tubes is membranous 

 rather than fibrous, though with the best glasses a fibrous striation may be frequently seen, 

 both in the laminae separating the different series of tubes, and in that dividing those of the 

 same layer from each other. By acetic acid, also, the structure swells, and displays corpus- 

 cles resembling those apparent in the white fibrous tissue. Such is the lamellar structure of 

 the cornea, which makes it so much easier to thrust an instrument horizontally than verti- 

 cally into its substance. The tubes or elongated spaces of which we have spoken, are not 

 distended with any fluid, but are merely moistened in the same way as the areolas of ordi- 

 nary areolar tissue. A perfectly fresh and transparent cornea is rendered opaque by pres- 

 sure, but it regains its brilliance on the removal of the compressing force. Some have sup- 

 posed this to result from the expulsion of fluid from between its laminae ; but that the opa- 

 city is owing simply to a derangement of the elementary parts of its structure is plain from 

 the fact, that the same phenomena are exhibited by a section, however thin, immersed in 

 water, and deranged by stretching.] 



190. In connection with the cornea, it is natural to allude to the Crystal- 

 line lens and Vitreous humour, which have a structure essentially the same. 

 The structure of the Crystalline lens has long been known to be fibrous ; and 

 Sir D. Brewster has shown, by the aid of polarized light, the very beautiful 

 manner in which the fibres are arranged.* They are united into laminae, by 

 means of numerous teeth or sinuosities at their edges, which lock into one 

 another. That these fibres originate in cells, has been clearly ascertained ; 

 but the nature of the metamorphosis has been differently stated by two emi- 

 nent observers, Schwann and Barry. By the former, the fibres are considered 

 to be prolonged cells : whilst the latter regards them as rather formed upon 

 the plan of the tubes of muscular fibre ( 235), several cells coalescing into 

 one ; in this he is supported by Mr. Toynbee, who states that he has fre- 

 quently seen the fibres, towards the margin of the lens, made up of such cells. 

 After it is fully formed, however, it is not permeated by blood-vessels ; these 

 being confined to the capsule. During the early part of fetal life, and in in- 

 flammatory conditions of this membrane, both the anterior and posterior por- 

 tions of the capsule are distinctly vascular; but at a later period, according to 



* Philosophical Transactions, 1833. 



