THE CORXEA. 715 



At its circumference the cornea joins the sclerotic part by continuity of tissue, 

 but always so as to be overlapped by the opacity of that structure like a 

 watch glass by the edge of the groove into which it is received. 



STRUCTURE. The cornea consists of a central thick fibrous part, the 

 cornea proper, covered in front by the conjunctival epithelium and the ante- 

 rior elastic lamina, and behind by the posterior elastic lamina or membrane 

 of Demours. 



The cornea proper is a stratified structure, the constituent fibres of which, 

 continuous externally with those of the opaque sclerotic, are soft and com- 

 paratively indistinct, and between the strata of which are numerous delicate 

 anastomosing nucleated cells, of fusiform appearance as seen in vertical sec- 

 tions, but expanded in the direction of the laminae, and presenting in sections 

 parallel to the surface a stellate appearance. The strata, about sixty in 

 number, at a given spot (Bowman),* maintain frequent communications with 

 contiguous layers, so that they can be detached only for a very short dis- 

 tance : in consequence of this stratified composition the cornea may be 

 penetrated or torn most readily in the direction of the supposed laminse. 

 The transparency of the cornea is impaired by derangement of the relative 

 position, or by approximation of the strata to each other. The cornea 

 proper is permeable to fluid, and affords chondrin, not gelatine, on boiling 

 (J. Miiller). 



There have been observed by v. Recklinghausen in the cornea of the frog, when 

 examined in a chamber of liquid connected with the microscope, not only a rich net- 

 work of anastomosing cells, but other cells also which change both their form and 

 position by means of processes thrown out from and disappearing again into their sub- 

 stance, like the pseudopods of amoebae. (Virchow's Archiv, Vol. 28, p. 157). 



According to Henle, the anastomosing cells of the cornea are mere spaces devoid of 

 any walls distinct from the surrounding matrix, and are the only interlaminar spaces 

 naturally existing. (Systematise-he Anatomic, Vol. ii. p. 599). 



The membranes investing the fibrous part of the cornea before and behind 

 are both of them structureless, with epithelium on their free surface. 



The anterior elastic lamina (Bowman) is a transparent glassy stratum with- 

 out recognised texture, from ^^^th to -y^^th of an inch thick, and not 

 rendered opaque by acids. From the surface resting on the fibrous strata of 

 the cornea, a few fine threads are prolonged in a slanting direction, and are 

 lost among the more superficial of those strata : their action is supposed to 

 be to keep the membrane tied down smoothly to the cornea. The epithelium 

 on the front of this lamina is stratified, the superficial cells being flat, and 

 the main thickness formed of three or four layers of rounded cells, the deepest 

 of which are vertically elongated, so as to be nearly twice as long as broad. 



It is right to mention that this epithelium in the horse, the ox, and the sheep, has a 

 much more remarkable appearance than in man, and one not to be accounted for by 

 the ordinarily presumed mode of growth of stratified epithelia ; for the deepest cells 

 are greatly elongated and larger than those which are immediately superimposed, and 

 have precisely the appearance of true columnar epithelium, the flat ends resting on 

 the subjacent elastic lamina, and the pointed extremities directed forwards. 



The membrane of Demours or Descemet (posterior elastic lamina, Bowman), 

 not very closely united with the fibrous part of the cornea, is transparent and 

 glassy in appearance, firm and structureless, but very brittle and elastic ; and 



* Lectures on the parts concerned in the operations on the eye, and on the structure of 

 the retina. London, 1849. 



