On the so-called choroid gland or choroid muscle of the fish's eye / by T. Wharton Jones.

  • Jones, Thomas Wharton, 1808-1891.
Date:
[1838]
Catalogue details

Licence: Public Domain Mark

Credit: On the so-called choroid gland or choroid muscle of the fish's eye / by T. Wharton Jones. Source: Wellcome Collection.

Provider: This material has been provided by The Royal College of Surgeons of England. The original may be consulted at The Royal College of Surgeons of England.

    1/2
    ON THE SO-CALLED CHOROID GLAND OR CHOROID MUSCLE OF THE FISH’S EY _ Y <t> By T. WHARTON JONES. \ [From the Medical Gazette.] About five years ago I examined the structure of the body in the eyes of fishes known by the name of the “ cho- roid gland,” or “ choroid muscle,” and obtained the following results:— When the sclerotica is removed from the back part of the eye of a fish, of a cod (gadus morrhua) for example, a silvery-like membrane is seen covering the posterior surface of the choroid coat. Tear this off, and a dark red swollen body, somewhat of the shape of a horse- shoe, and encircling irregularly the entrance of the optic nerve, will be ex- posed. This body, the relief of which can be seen before the removal of the silvery-looking membrane, is the so- called choroid gland or choroid muscle. Its extremities meet, but are not incor- porated together, at the line or fissure which runs from behind, forwards, along the lower half of the eye. A fine aponeurotic-looking expansion covers the body. A great number of large vessels are connected with the outer edge of the so-called gland or muscle, and a little careful examination will show that ves- sels enter by its inner edge also.—How do these vessels comport themselves ? Examined with a magnifying glass, it will be discovered that at either edge the vessels, after subdividing to a con- siderable degree of minuteness, anasto- mose with each other, and form a net- work. If now we subject the central substance of the body to microscopical examination, we shall find it is com- posed of an aggregation of minute straight vessels running across and con- nected by their extremities with the plexus on either edge of the body. Close by the optic nerve two blood- vessels are connected with the eye ; one of these, thicker in its coats and a little larger than the other, an artery, after having entered the eye divides into two branches which run along the inner edge of the body, giving off twigs which by their subdivision and anastomoses form the net-work already mentioned at the inner edge. From the minute plexus at the outer edge vessels emerge, which run together to form larger twigs. The latter enter pretty considerable trunks, which at first skirt the outer edge of the body, but afterwards turning away from it, proceed forwards and ramify in the choroid coat. The vessels which emerge from the outer edge of the body have very thick fleshy-looking coats. The minute ves- sels forming the central substance of the body, have also thick coats; on account of which circumstance, and on account of their straight parallel course betwixt the two net-works, the body, when torn, presents a fibrous structure. And this structure, on account of the red colour, (which is derived, in a great degree, though not entirely, from the blood globules the vessels contain), simi- lates very much the appearance of mus- cular fibre. It is easy to inject with mercury the artery entering the eye as far as the network, on the inner edge of the body; but I have not found the mercury go across to the network at the outer edge. Sometimes, however, a minute globule may be pressed across. After this description there can be little doubt but that the so-called cho- roid gland or muscle of the fish’s eye is a tissue of vessels—that it is in fact a rete mirabile. But this is not the only rete mirabile in the eye of the fish, for the arteries as they proceed forward in the choroid, many of them, subdivide into small branches, which again unite into one, thus forming secondary and more simple retia mirabilia. Lastly, the arteries of the choroid terminate in