Explanation of figs. on Plate XIII:

Fig. 1. V. S. cornea of albino rabbit, hardened in a mixture of chromic acid aind spirit; a, corneal epithelium; b, cornea proper; c, elastic lamina, posterior epithelium removed; d, clear hem on corneal epithelium.

Fig. 2. a, various forms of cells from lowest layer of columnar epithelium isolated by iodised serum; b, similar cells; c, bases of a and b; d, 'digitate' cells from higher layer; e, prickle cells further up towards surface of cornea.

Fig. 3. Peculiar appearance sometimes seen in vertical sections of cornea of ox; a, tall compressed cells; b, similar cells swollen out and compressing a.

Fig. 4. Corneal epithelial cells of ox isolated by iodised serum; a and b, lowest layer of cells; b. apex grasped by fangs of a digitate cell; c, ' digitate' cells; d, smaller digoitate cells higher up; e, prickle cells.' (338)

Fig. 1 in text:

'On examining a vertical section of a cornea which h, as been stained with picro-carmine and mounted in glycerine, we get such a view as is shown in Fig. 1, Pl. XIII., where a represents the epithelium covering the anterior surface of the cornea proper, b; c the posterior elastic lamina. The picro-carmine has stained the nuclei of all the cells red, their substance yellow, and the cornea proper and elastic lamina red.' (335)

'Fig. 1 d is very instructive, for it shows a part of the corneal epithelium detached from the cornea proper, each cell showing its clear hem.' (336)

Fig. 2 in text:

'The columnar cells forming the lowest layer are not all of the same height, nor of the same size, as generally represented. This is well brought out in Fig. 2, a and b, and Fig. 2 c shows the bases of these cells, and here we note that they are not all of the same size at the base...

The lowest columnar cells are always slightly expanded at their bases, and the clear band is not so marked as after hardening. Their appearance is shown in Fig. 2 a, taken from a preparation isolated by iodised serum. From the middle layers a few prickle cells are always obtained of various forms, and Fig. 2 b shows the difference in the height of these cells. From above this layer we have succeeded in isolating smaller cells-digitate cells, whose teeth fit in between and grasp the apices of several columnar cells. We shall allude to these more fully presently. Prickle cells can also be easily isolated, Fig. 2 e.' (336)

Fig. 3 in text:

'Fig. 3 gives a view of a section of the cornea of the ox... but certain of the appearances however are peculiar and apt to lead one into error, unless controlled by examining other preparations. Every here and there groups of short broad cells (b) are to be observed, occurring between groups of tall cells (a). This is not a normal appearance but due to the swelling out of those at b compressing those at a, and thus giving rise to this peculiar appearance, which we have also seen in the rabbit's cornea.' (337)

Fig. 4 in text:

'We find that Rollett [note: 'Rollett, article Cornea in Stricker's Histology, English Edition, p. 424.'] has also noticed in the lowest layer of cells of the cornea of some animals a basal 'hem' or 'border'... He says, "The expanded basal borders of the cells are so applied to each other, or are so superimposed upon one another by their thin edges, that the borders of the several cells seen collectively in situ make a bright stria which forms the line of demarcation between the epithelium and the corneal tissuet." [note: 'L.c. p. 427.'] This is also the view we take of the matter, for the base of each cell is always expanded somewhat and broader than the part immediately above the base (Fig. 4, a and b).

We now proceeded to isolate the cells from the cornea of the ox by means of iodized serum. Fig. 4, a and b, shows the lowest layer of columnar cells. They are very remarkable on account of their being so elongated; they are as elongated as any epithelium in the body .Invariably their base is flat as described by Prof. Cleland [note: 'On the Epithelium of the Cornea of the Ox, Journal of Anat. and Physiology, Vol. II. P. 362.']... The clear hem is very delicate and not nearly so pronounced as in the rabbit. Above these cells Prof. Cleland in 1867 described cells of peculiar shape, to which he gave the name 'digitate'. "They are of irregular shape, about twice as broad as the columnar epithelium, but by no means so elongated." He describes them as " rounded and even in outline at the superficial extremity," (but they are not all so (Fig. 4 c), though some are,) and "jagged at the other, and send in processes or 'digitations', which may be three or four in number, and which appear to fit in between the tapering points of the columnar cells." We have directed especial attention to these peculiar 'digitate' cells, for their existence has been denied by Rollett [note: 'Op. c. p. 424'], but there cannot be the slightest doubt of their existence... They present much the appearance of a molar tooth with its fangs, dipping in between the apices of the columnar cells, and Fig. 4 b shows how they are placed, each cell being in relation with the apices of several columnar cells.' (337-338)

'Above this layer of digitate cells we have a stratum of smaller cells some of which are 'digitate' (Fig. 4 d), and there is a gradual transition between them and small prickle cells (which occur in very large numbers in the cornea of the ox and sheep), and gradually as we pass upwards we come to the large flat squames on the surface.' (338)