An American text-book of diseases of the eye, ear, nose and throat / edited by G.E. De Schweinitz and B. Alex. Randall.

Date:
1899
Catalogue details

Licence: Public Domain Mark

Credit: An American text-book of diseases of the eye, ear, nose and throat / edited by G.E. De Schweinitz and B. Alex. Randall. Source: Wellcome Collection.

Provider: This material has been provided by the Harvey Cushing/John Hay Whitney Medical Library at Yale University, through the Medical Heritage Library. The original may be consulted at the Harvey Cushing/John Hay Whitney Medical Library at Yale University.

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    innermost stratum are deeply pigmented, in consequence of which the inner surface of the .sclerotic coat presents a dark color and is known as the lamina fusca: this layer constitutes the (inter wall of the subscleral lymph-space, and is attached to the subjacent choroid by numerous trabecular, which, together with the limiting walls of the space, are covered with endothelial plates. The greater extent of the outer surface of the sclera, from the sheath of the optic nerve to the insertion of the ocular muscles, is also clothed with endothelium, which forms part of the lining of the episcleral space of Tenon. The blood-vessels of the sclera, in addition to the perforating vessels, which include anterior branches from the anterior ciliary vessels, the large equatorially situated vena? vorticose, and posterior branches from the posterior ciliary vessels, are represented by the meager twigs within the superficial strata of the fibrous tunic derived from the wide-meshed episcleral network formed by branches derived from the anterior and posterior ciliary arteries. The sclera receives additional branches from the short ciliary arteries in the vicinity of the optic entrance : these small vessels arc of interest, since from the circulus Zinnii, which they form within the fibrous coat around the optic nerve, minute twigs extend into the dural nerve-sheath and anastomose with the arterioles supplying the sheath derived from the central artery of the retina, thus establishing a communication between the retinal and cho- roidal circulation. The veins which drain the scleral coat are tributary to three sets of vessels: those from the anterior tract, emptying into the anterior ciliary veins ; those from the equatorial zone, joining the vena? vorticosae; and those from the posterior part, pouring their blood into the posterior ciliary veins. The lymphatics of the sclera are represented by the system of intercom- municating scleral spaces, those in the vicinity of the sclero-corneal juncture being in close relation with the spaces of Fontana at the angle of the anterior chamber, which they indirectly aid in draining. The nerves distributed to the sclerotic coat consist of a few twigs derived from the ciliary nerves as these pass between the sclera and choroid, which terminate between the fibrous bundles of the superficial layers as tortuous and intricately coursing ultimate fibrillar. The relations of the scleral tissue to the sheaths surrounding the optic nerve will be considered with the description of the Optic Entrance. The Sclero-corneal Juncture.—The position at which the sclera and corneal segments of the fibrous coat meet is one of the most important regions of the eye, since in the immediate vicinity of this junction lie important channels through which escapes the aqueous humor as well as the fibers giving origin to the ciliary muscle. The conspicuous line of union between cornea and sclera depends far more upon the physical differences of the two portions of the fibrous coat than upon actual structural variation, since the elements are not only almost identical, but directly continuous. When seen in section the scleral tissue extends along both margins farther forward than does the corneal substance, the effect of this arrangement being to receive the cornea with an apparent annular groove bounded by the outer and inner scleral processes: of these the inner is shorter and does not reach as far toward the anterior pole as the outer. The connections of the inner scleral process are of especial importance on account of the relations to the structures marking the meeting of the cornea, the iris, and the ciliary muscle. Just anterior and external to the