730 SPECIAL HISTOLOGY. 



0'006-0'01 of a line in size, with extremely fine and pale granular 

 contents, and round nuclei of 0-003-0-005 of a line. Towards the 

 border of the cornea the cells of which the epithelium is constituted 

 become smaller, and then ceases as a connected layer, whilst isolated 

 indications, usually of elongated, or even fusiform epithelial cells, are 

 continued, over the fibrous network of the lig. pectinatum, and sur- 

 rounding its elements, upon the border of the iris, where a perfect 

 epithelium is again met with.* 



The cornea in the adult is nearly altogether non-vascular, whilst, as 

 J. Miiller and Henle first observed (" De membr. pupilL," p. 44), in 

 the human embryo and foetal Lamb a rich capillary plexus exists in the 

 conjunctiva cornea?, but which does not appear to extend as far as the 

 centre. Towards the end of foetal life and after birth, this plexus dimi- 

 nishes in breadth, in animals to a less extent than in Man, so that in 

 the latter we find bloodvessels at the margin of the cornea, only in a 

 zone of J- or at most of 1 line in width. These vessels are for the most 

 part the fine and finest capillaries of 0-002-0-004 of a line, forming one 

 or several rows of arches, and thus terminating ; they are lodged in the 

 substance of the conjunctiva, which here extends, in the form of a dis- 

 tinct layer, for a short distance upon the cornea, ceasing in its anterior 

 structureless lamella. In animals these superficial or conjunctival vessels 

 aho exist, but are usually much better displayed, and extend further 

 towards the centre ; frequently over half the radius, or even beyond it. 

 Besides these, deeper capillaries derived from the sclerotic also occur in 

 the substance of the cornea, usually accompanying the nervous trunks, 

 in which they either form a single or a few very much elongated loops, 

 or extend a little beyond^ them ; they all terminate in loops, the finest 

 vessels constituting which, like the superficial capillaries, measure 

 scarcely more than 0-002 of a line. I have also noticed, in Man, these 

 peculiar corneal vessels accompanying the nervous trunks, although not 

 constantly and never so much developed. 



Nothing certain is known of the lymphatics of the cornea (vid. also, 

 Arnold, "Anat." II. p. 988), though I have recently observed vessels 

 in the cornea of a young Cat (Fig. 297), which I can scarcely regard 

 as anything else than lymphatics. In this instance, at the margin of 

 the cornea, together with the very distinct capillary loops containing 

 blood-corpuscles, there were numerous wider vessels (of 0-01-0-02, or 

 even 0-03 of a line), which either extended singly into the cornea to the 



* [This statement is directly opposed to Mr. Bowman's observations (op. c., p. 22). who 

 says, " that it would appear from what has been said concerning the conversion of the pos- 

 terior elastic lamina at its border into fibrous tissue, which in part passes through the 

 aqueous humor to the iris, that this epithelium must cease with the elastic lamina, since 

 there is no longer any stratum upon which it can rest." He has been unable " to discover 

 the smallest appearance of it upon the pillars of the iris, and conceives, therefore, that it is 

 limited to the cornea." And according to the same accurate observer, the front of the iris 

 has no true epithelial investment. Tus.] 



