For the description of the bones composing the foot, we refer to the article under that head ; and for further details on the osseous system of the extremities, we refer to the articles OSSEOUS SYSTEM (Comp. Anat.) and SKELETON.
Abnormal condition of the bones of the artre ?I:X(1.—A congenital malformation of one or more of the extremities is classed by Isidore Geoffroy St. Hilaire among what he denomi nates " Monstres Ectromeliens," of which he has three subdivisions : 1st, where the hands or feet appear to exist alone, and seem to be connected with the trunk without the inter vention of all or some of the intermediate segments; these he denominates Phocomelcs, ((panel!, Phocu, and /hag, membruni,) from their resemblance to the permanent condition of the aquatic manunalia : 2d, cases in which there are one or more incomplete limbs terminating in the form of stumps : to these he gives the name llonimeles: and, lastly, where the limb or limbs are wholly absent or scarcely at all developed. An interesting case of Phoco melia is recorded by Durneril ; all the limbs were in this condition, owing to the absence of the humerus, and forearm bones in the upper extremity, and the presence of a very imperfect femur, developed only as to the head and tro chanters, and a very imperfect tibia in the lower extremity. The clavicle and scapula were pre sent, but presented some irregularities of form.* The congenital absence of these last bones is rare excepting where the other bones of the limb are also absent.
It would be inconsistent with the objects of this article to prosecute this subject further ; we therefore refer for further details to the article MONSTROSITY.
EYE, (in human anatomy), ocOaiip.oc, orga non visas ; ocutas. Fr. ; Germ. dos Auge ; Ital.Oechio.—The human eye is a hollow sphere, about One inch in diameter, with a circular aperture in the anterior part about one-fifth of this sphere in breadth, filled by a transparent convex portion called the cornea, through which the light is transmitted. Within this hollow sphere, and at a short distance behind the trans parent convex portion or cornea, is fixed a double convex lens, called the crystalline lens or crystalline humour; and between this cor nea and crystalline lens is interposed a parti tion or screen called the iris, with a circular aperture in its centre called the pupil. The inner surface of this hollow sphere, as well as the back of the iris or screen, are covered or stained with a black material. The space be tween the cornea and crystalline lens, in which the iris is placed, is filled with a transparent fluid, called the aqueous humour, and the space between the crystalline lens and the bot tom of the sphere is filled with a similar fluid, called the vitreous humour. The annexed figure represents a section of this simple piece of opti cal mechanism, much larger than natural to render the parts more distinct.
An acquaintance with the laws which regu late the transmission of the rays of light through transparent bodies, and with the manner in which the lenticular form changes the direction of these rays, teaches that a correct image of ex ternal objects is formed in the bottom of the eye in consequence of the above adjustment of its parts. First, the rays of light acquire a con vergence in their passage through the cornea and aqueous humour, then the central portion of the pencil of rays is transmitted through the pupil, and, finally, the rays in their passage through the crystalline lens acquire such addi tional convergence, that they are brought to a focus on the bottom as represented in the an nexed diagram.
Such are the essential component parts of the eye, considered as a piece of optical me chanism, but viewed as a piece of anatomical mechanism, its construction is much more com plicated, and the materials of which it is com posed are necessarily totally different from those of any human contrivance of a similar nature.
It lives in common with the body of which it forms a part, it grows and is repaired ; conse quently, the animal organisation destined for such functions must constitute an essential part of its construction.
The organ derives its permanent spherical form, its external strength, and the support of the delicate parts within it, from a strong opaque membrane called the sclerotic coat; while the convex portion, called cornea, in front, equally strong, being transparent, allows the rays of light to pass without interruption. The interior of the portion of the sphere formed by the sclerotic coat is lined throughout by a soft membrane called the choroid, necessarily con stituting another hollow sphere, accurately adapted and adhering to the inside of the for mer. This also has its circular aperture ante riorly, into which is fitted the screen called iris, as the cornea is fitted into the aperture in the sclerotic. While the external surface of this choroid coat is comparatively rough and coarse in its organization, as it adheres to the equally coarse surface of the sclerotic, the interior is exquisitely smooth and soft, being destined to embrace the retina, another spherically dis posed membrane of extreme delicacy. The screen called iris, which is fitted into the cir cular aperture anteriorly, is as different from the choroid coat in its organization.as the cor nea is from the sclerotic: it is perfectly plane, and therefore forms with the concave surface of the cornea a cavity of the shape of a piano convex lens, called the anterior chamber. In or on the choroid coat the principal vessels and nerves, destined to supply the interior of the organ, are distributed, and in its texture and upon its inner surface is deposited the black material, which in this part of the chamber, as well as on the back of the iris, is so essential a provision. At the anterior margin the choroid is more firmly united to the corresponding mar gin of the sclerotic by a circular band of pecu liar structure called the ciliary ligament, and on its inner surface, in the same place, it is fur nished with a circle of prominent folds called ciliary processes, by means of which it is united to the corresponding surface of the hyaloid membrane of the vitreous humour. The an nexed figure represents a section of this hollow sphere lodged within the sclerotic sphere. The external circle, a a, between the two black lines represents a section of the strong opaque membrane called the sclerotic, which consti tutes the case or resisting sides of the organ ; is the transparent lenticular window called cornea, which fills the aperture left in the ante rior part of the sclerotic for its reception ; d d is the place of union between the sclerotic and cornea, to which the ciliary ligament on the outside of the anterior margin of the clioroid sphere corresponds ; e e the circle bounded by the line marking the inner surface of the sclerotic externally, and by the shaded part in ternally, represents a section of the hollow sphere called choroid. At the point d d, cor responding to the place of union between the sclerotic and cornea, this choroid projects exter nally, encroaching upon the sclerotic in a pecu liar manner, to be presently described as the ciliary ligament ; while at the same point it projects internally in the shape of a series of folds, to be described as the ciliary processes. The white productions extending from the same points in a vertical direction into the chamber of the aqueous humour, between the cornea and crystalline lens, represent a section of the screen called the iris. f is a section of the crystalline lens.