Sclerotic conjunctiva, conjunctiva scleroticie. As far as vascularity goes, there is a decided difference between this and the preceding. The sclerotic conjunctiva is composed of a chorion or vascular basis of the membrane covered by epithelium. Valentint describes between the chorion and epithelium another structure which he calls papillary.
The chorion of the sclerotic conjunctiva con sists of irregularly stratified fibres of cellular tissue interwoven with bloodvessels and nerves.
" Do the conjunctiva sclerotiem and the conjunctival pellicle of the cornea also preserve a papillary body or not?" asks Eble,t in re ference to Valentin's assertion of one. Eble admits the structure described by Valentin under the name of papillary body between the chorion and epithelium of the conjunc 'tiva bulbi, but thinks, and correctly, that it is a very different thing from the papillary body of the palpebral conjunctiva as described by himself. Valentin's papillary body of the con junctiva bulbi is a matter of the microscope Eble's papillary body of the palpebral con junctiva, though minute, is still in some de gree cognisable to the naked eye. Hypertrophy of the papillary body of the palpebral conjunc tiva constitutes, as has been said, what is called granular conjunctiva. We never see such a gra nular state of the sclerotic conjunctiva.
The following is Valentin's description of what he calls the papillary body of the conjunc tiva bulbi :—It is best seen in the human eye, " when, after several days' maceration, the loosened and swollen epithelium is carefully removed and the papillary body then separated by a shaving cut through the surface of the conjunctiva. The papilla are seen under a microscope magnifying three hundred diame ters, as yellowish red corpuscles standing close together, of an arched conical shape and pre seining a round nucleus in their interior. Many of the papillae have short pedicles. Many present at their extremity a small point or fila mentous prolongation which runs towards the epithelium. IIenle* thinks Valentin's papilla are nothing but the corpuscles of the epithe lium, presently to be noticed, distorted by the action of the compressorium. It appears to me that Valentin's papillary body constitutes a structure of the same nature as the corpus Malpighianum of the skin. We know that such exists in the sclerotic conjunctiva from the circumstance that in negroes and many of the lower animals it is tinged of a black or brown colour, whilst in Isabella horses and in Swiss races among oxen it appears yellowish.
Epithelium of the conjunctiva. The dis covery of a characteristic structure in epithe lium enables us to determine its existence even when so delicate as not be separable as a dis tinct layer. It may appear merely as a tena cious mucus little more than perceptible to the naked eye, but examined under the microscope it is found to consist of minute polygonal cells, flat and containing a central nucleus. These corpuscles aggregated together more or less closely and in greater or less quantity con stitute the substance of epithelium. The epi dermis is essentially of the same structure; as also the corpus Malpighianum, only when this is coloured, the cellules are found to contain colouring particles, as is remarkably the case in the black pigment of the eye, the small hexagonal bodies composing the membrane of which belong to the same category as the cor puscles of the epithelium or corpus Malpi ghianum.
According to Valentin the epithelium of the conjunctiva consists of rhomboidal or quad rate cells lying close together, the boundaries of which are formed by simple lines. In every cell there is found without exception a some what darker and more compact nucleus of a round or largish form. The average diameter of these cells, in the human eye, is about the two-thousandth of an inch. The nuclei are about half the size.
Thickening of the epithelium takes place in ectropium and callous granulations. What is called cuticular conjunctiva is at the same time a general contraction of the whole conjunctiva with a thickened and dry state of the epi thelium.
Does the conjunctiva extend over the cornea? ' Every one admits the existence of a layer on the anterior surface of the cornea, quite dif ferent from its proper substance, and apparently a continuation of the conjunctiva covering the sclerotica, but this layer on the anterior surface of the cornea does not present exactly the same, or at least all, the anatomical and chemical characters as the sclerotic conjunctiva. What of it can be raised is like epidermis or epithe lium, coagulated and rendered white by the heat applied to separate it, and moreover it is not vascular, the vessels seen ramifying on the surface of the cornea in some inflammations being situated underneath it.