Volume 2

Manual of practical anatomy / by D.J. Cunningham.

  • Cunningham, D. J. (Daniel John), 1850-1909.
Date:
1903
Catalogue details

Licence: Attribution-NonCommercial 4.0 International (CC BY-NC 4.0)

Credit: Manual of practical anatomy / by D.J. Cunningham. Source: Wellcome Collection.

Provider: This material has been provided by The University of Leeds Library. The original may be consulted at The University of Leeds Library.

    593/652 (page 569)
    posed of a posterior opaque part, called the sclerotic coat, and an anterior clear transparent portion called the cornea; (2) an intermediate vascular envelope, in which we recognise three subdivisions, viz., a hinder part called the choroid coat, a front portion termed the iris, which lies behind the cornea, and an intermediate ciliaty zone; (3) the nervous inner tunic or retina in which the fibres of the optic nerve spread out. The refracting media are: (i) behind the cornea a watery fluid, called the aqueous humour, contained in a space partially subdivided by the iris into the tivo chambers of the eye J (2) the crystalline lens behind this; and (3) the vitreous body, occupying the posterior part of the interior of the eyeball. Dissection.—The superficial surface of the sclerotic coat and the cornea should now be examined ; but to complete the study of the external tunic, a further dissection is required. Selecting'an eyeball for this purpose, an incision should be made with a sharp knife through the sclerotic at the equator. This must be done carefully, and the moment that the sub- jacent black choroid coat appears the knife should be laid aside. The cut edge of the sclerotic should now be seized with the forceps, and the incision carried completely round the eyeball with the scissors along the line of the equator. The outer fibrous tunic is thus divided into an anterior and a posterior portion. These must now be raised from the subjacent parts. As the anterior portion is turned forwards, some resist- ance will be met close to the margin of the cornea from the attachment of the ciliary muscle to the deep surface of the sclerotic. This can easily be broken through with the blunt point of the closed forceps ; as soon as this is done the aqueous humour escapes. In the case of the posterior part of the sclerotic, its complete separation can be effected by dividing the fibres of the optic nerve close to the point where they appear through the sclerotic. When_ the above dissection is successfully carried out, the outer fibrous tunic is isolated in two portions, whilst a continuous view of the inter- mediate vascular coat is obtained. The eyeball, denuded of its external tunic, should now be placed in a shallow vessel filled with water. Sclerotic Coat.—The sclerotic is what is commonly known as the white of the eye. It is a dense, resistant tunic, opaque-white in colour, which envelops the posterior five- sixths of the globe of the eye. It is thickest behind, and becomes thinner as it is traced forwards. Near the cornea, however, it again becomes thicker owing to the accession of fibres which it receives from the tendons of the ocular muscles. Except at the optic entrance and close to the margin of the cornea, where it adheres to the surface of the subjacent ciliary muscle, the deep surface of the sclerotic is