360 SPECIAL HISTOLOGY. 



hibit, though rarely, bifurcations of the primitive tubules, but 

 divisions of this kind are never presented in the plexus formed 

 by them, the conditions in which, however, on account of 

 their paleness, scarcely admit of being quite certainly traced. 

 This plexus is situated in the 'proper cornea, although nearer 

 to its anterior surface, and from the absence of any indication 

 of free terminations to the nerve-fibres, appears to consist 

 altogether of anastomosing branches of the finest sort, so that, 

 though not in the form of loops, a mutual connexion of the 

 nerve-tubes may be assumed to exist. 



[The blood-vessels of the conjunctiva cornea, in the healthy 

 condition of the organ, are very scant}', and the figures given 

 by Romer (Amnion's < Zeitsch.' V, 21, Tab. I, figs. 9, 11) and 

 Arnold (' Icon. org. sens/ II, fig. 6), I regard as exceptional 

 instances; but, as is well known, they may become so much 

 developed, in inflammations, as almost to cover the entire 

 cornea. The proper corneal vessels also, in such cases, appear 

 to be developed more deeply in the interior. With regard to 

 the vasa serosa of the cornea, vid. § 217. The statements 

 that have been made respecting the blood-vessels of the mem- 

 brana Demoursii, in inflammation of the eye (vid. Henle, ( De 

 memb. pupill/ p. 53), appear still to demand confirmation; and 

 Arnold's " serous vessels/' in the normal condition of the 

 membrane of Descemet ('Anat/ I, Tab. II, fig. 5, II, p. 1015), 

 are nothing more than the anastomosing fibres of the liga- 

 mentum pectinatum of the iris. The cornea, although vascular 

 only at its margin, is nevertheless not unfavorably circum- 

 stanced as regards its nutritive conditions. Wounds in it 

 rapidly unite, portions of the epithelium or even of the fibrous 

 layer when removed, are restored, and ulcers are filled up from 

 the bottom with new corneal substance. Fatty deposits in its 

 tissue, particularly in its cellular elements (especially above 

 and below, or even all round), produce a yellow zone — the 

 so-termed arcus senilis (gerontoxon)}~\ 



§ 226. 

 The vascular tunic {tunica vasculosa) or uvea. — The second 

 tunic of the eye-hall is a highly vascular membrane, containing 



1 [As shown by Mr. Edwin Canton in his ' Observations on the Arcus senilis, or 

 fatty degeneration of the Cornea.' — 'Lancet,' vol. i. 1850, p. 560. — Eds.] 



