SECT. 225.] THE CHOROID. 545 



figs. 9, 11), and Arnold (Icon. Org. Sens, ii., fig. 6), I regard as exceptional 

 cases ; but, on the other hand, as is well known, these vessels become so 

 developed in inflammations, that they cover the whole, or almost the whole, 

 cornea. The proper vessels of the cornea likewise appear in such cases to ex- 

 tend further inwards. "With regard to the vasa serosa corneoe, I would refer to 

 my Micr. Anut. ii., 2, p. 624, et seq. — The cornea, although vascular only at the 

 border, is still not unfavourably placed with reference to its nutrition. 

 "Wounds of the cornea readily heal ; portions of the epithelium or even of the 

 fibrous layer are restored after removal, and ulcers fill up from the bottom 

 with new corneal substance. Depositions of fat in its tissue, especially in its 

 cellular bodies, produce at the border (especially above, but also at the lower 

 margin, or even round the entire circumference), a yellow zone, the so-called 

 'arcus senilis' (gerontoxon). In all pathological alterations of the cornea, as 

 His has clearly shown, the cells of the cornea play a chief part, especially by 

 their enlargement, and by the production within them of numerous nuclei or 

 endogenous cells, a change on which all subsequent metamorphoses appear to 

 follow (His, 1. c, pp. 73 — 140).— On the membrane of Descemct peculiar w r arty 

 excrescences are occasionally found, and to a slight degree this appearance 

 is not uncommon even in healthy eyes (H. Mutter). 



§ 225. Vascular Tunic or Uvea. — The second tunic of the eye- 

 ball is an extremely vascular structure, containing a large amount 

 of pigment, and may be divided into a larger posterior section, the 

 choroid, and a smaller anterior portion, the iris. 



The choroid coat extends forwards from the place of entrance of 

 the optic nerve as far as the iris, with which it is continuous. In 

 the former situation it presents a circular aperture, but is con- 

 nected with the neurilemma of the optic nerve, and passes trans- 

 versely through the nerve in the form of a delicate cribriform 

 layer. The choroid is a fragile membrane ^" to ~^" thick, but 

 at the anterior border of the sclerotic it forms a thicker part, the 

 corpus ciliare. Its outer surface is pretty intimately attached to 

 the sclerotic, not only by the larger vessels and nerves, but also by 

 other means, so that on exposing the choroid, a part of it, of 

 greater or less extent, remains fixed on the sclerotic as a delicate 

 brown tissue. This is the so-called lamina fusca of authors, but 

 there is no sufficient reason for separating it from the choroid and 

 describing it as a special coat ; although it is true that separate 

 pigment cells, such as occur in it, do often extend in among the 

 connective tissue of the sclerotic. The inner surface of the choroid 

 is smooth, and is connected with the retina very firmly at the ora 

 serrata, but is only loosely adherent in the rest of its extent : on the 

 other hand, in front of the ora serrata, on the ciliary processes 

 particularly, it is very intimately united with the pars ciliaris retinae, 



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