An inaugural essay, on the eye, and on vision : submitted to the examination of the Rev. John Andrews ..., the Trustees and medical professors of the University of Pennsylvania, on the 5th day of June, 1805, for the degree of Doctor of Medicine / by Elisha de Butts, of Maryland.

Date:
1805
Catalogue details

Licence: Public Domain Mark

Credit: An inaugural essay, on the eye, and on vision : submitted to the examination of the Rev. John Andrews ..., the Trustees and medical professors of the University of Pennsylvania, on the 5th day of June, 1805, for the degree of Doctor of Medicine / by Elisha de Butts, of Maryland. Source: Wellcome Collection.

Provider: This material has been provided by the National Library of Medicine (U.S.), through the Medical Heritage Library. The original may be consulted at the National Library of Medicine (U.S.)

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    its strength. The sclerotic coat seems to be formed by the ex- pansion of the inner plate of the dura mater of the optic nerve ; the outer plate forming the periosteum of the orbit.* The se- cond coat, or the choroides, originates from the white cellular circle terminating the substance of the optic nerve t; and ex- panding, concentrically, within the sclerotica, is connected to it by vessels and cellular membrane. But at the circumference of the cornea, this cellular substance becomes much more dense, attaching the coats very firmly to each other, and is then called the ciliary band. The choroides, at this place, gives out, from every part of the circumference, certain radii, inter- intermingled with vessels, which, terminating at equal distan- ces from the centre, leave a small hole, called the pupil, to admit the rays of light. Round the pupil, and connected to the above radii, are certain fibres, disposed in the form of a ring, which act as a sphincter muscle, \ the former dilating, the latter contracting the pupil. The anterior surface of this part of the choroides, is termed the iris. The posterior, from its uniform resemblance, in colour, to a ripe grape, the uvea ; but this circumstance alone can make any difference between them. The iris varies in colour, in different people, and be- fore those ages of the world, when, in consequence of war or commerce, nations intermingled indiscriminately with each o- ther, the colour of the iris was invariably peculiar to the inhab- itants of different climates. In persons of fair hair and com- plexion, it is generally of a grey or blue colour, and in those who have black or dark hair, it generally observes various shades of hazle. The choroid coat is, externally, of a brown colour, and internally, is covered by a fine black pigment, ad- hering slightly to its surface. From the ciliary band, and im- mediately behind the uvea, the choroides produces, transc- versely and backwards, an extremely fine membrane, to be * KaUer on Phys. Chap. 16. p. 247. f Ibid, Chap.. 16. fi. 248. .J Monroe on the Eye.