Practical anatomy: a manual of dissections / by Christopher Heath.

  • Christopher Heath
Date:
1870
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Licence: Public Domain Mark

Credit: Practical anatomy: a manual of dissections / by Christopher Heath. Source: Wellcome Collection.

Provider: This material has been provided by the Francis A. Countway Library of Medicine, through the Medical Heritage Library. The original may be consulted at the Francis A. Countway Library of Medicine, Harvard Medical School.

    545/600 (page 535)
    the cornea will be rendered white and opaque, but will resume its former appearance when the pressure is relaxed. The Cornea (Fig. 243, i) is one of the transparent media of the eye ; and in man is perfectl}' circular when seen from within, but appears wider transversely from without, on account of tlie greater overlapping of the sclerotic above and below. The curvature of the cornea varies in different individ- nals, but the anterior and posterior surfaces are always parallel. The cornea is divisible into five layers: 1, ante- rior epithelium (conjunctiva); 2, anterior elastic lamina; 3, cornea proper; 4, posterior elastic lamina; 5, posterior epithelium (of aqueous humor) [membrane of Descemet or Demours. (Fig. 246, m d, p. 539.)] The cornea in health is a non-vascular structure, no bloodvessels existing in it, and its nourishment being derived from the surrounding structures. Minute branches of the ciliary nerves have however been traced into and through it. [The anterior epithelial la3^er of the cornea is readily demonstrated by rubbing the cornea b}^ the finger-nail or knife when it will be scraped off; if indeed it be not already detached at points. That this structure is really cutaneous, is shown in serpents, by its being shed along with the skin.] Holding the eye lightly with the left hand, the scalpel is to be thrust through the margin of the cornea into the anterior chamber, when the aqueous humor will necessarily escape. With scissors the cornea may then be removed [up to the very edge. It is always best in dissecting the eye to use the probe-pointed blade of the scissors such as are furnished now in our American dissecting cases.] The Anterior Chamber (Fig. 243, 3) is the space be- tween the cornea and the iris. It communicates with the posterior chamber through the pupil, and is filled with the aqueous humor. The Iris (Fig. 243, 2) is the highly vascular [and mus- cular] curtain which separates the anterior from the poste- rior chamber. [Its outer circular border is attached to the ciliary ligament at the sclerotico-corneal border, and will be better seen at a later stage of the dissection, (p. 537).] It is composed of involuntary muscular fibres, bloodvessels, and pigment, and may be considered to be a prolongation of the choroid coat. In man the pigment of the iris is of various colors, but it is absent altogether in albinos, and occasionall}^ the iris itself is wanting. The Pupil is a cir-