Haller, speaking of the choroid in fishes, says, " this organ is a fleshy pulp, composed of short columns densely consolidated, resembling red gelatine." Cuvier says," its colour is com monly a vivid red, its substance is soft and more glandular than muscular ; at least fibres cannot be distinguished on it, although the bloodvessels form more deeply coloured pa rallel lines on its surface. Its form is com monly that of a small cylinder bent like a ring round the nerve, which ring is not, however, complete; a segment of greater or less length is always deficient. Sometimes, as in the Perca labrar, it is composed of two pieces, one on each side of the optic nerve. In other cases it is not in a circle but an irregular curve, as in the Salmon, Tetradon mola, and Cod; but in the carps and most other fishes it approaches to to a circle. Those who suppose that the eye changes its figure according to the distance of objects, think that this muscle is destined to produce this effect by contracting the choroid ; but it appears to me that the numerous vessels passing out of it should rather lead to its being considered a gland destined to secrete some of the humours of the eye. These vessels are white, fine, very tortuous, and appear to traverse the tunica Ruyschiana; they are well seen in the Te tradon mole and Perca labras. In the Cod they are very large, anastomose together, and are covered by a white and opaque mucus. This gland does not exist in the cartilaginous fishes, as the Rays and Sharks, in which it approaches more to the character of the eye in the Mam malia, as has already been observed in speak ing of the tapetum and ciliary processes." D. NV. Summering says, " Around the insertion of the nerve is seen a peculiar red, thick, soft body of a horse-shoe shape, respecting which it is doubted whether it be muscular, glandular, or merely vascular. It is undoubtedly ex tremely vascular, and contains many large, branching, inosculating vessels, forming a proper membrane gradually becoming thin, and terminating at the iris. This vascular membrane constitutes the second or middle layer of the choroid." This description applies to the eye of the Cod. Sir E. Home, in a Croonian lecture published in the Philoso phical Transactions for 1796, says that Mr. Hunter considered the organ in question to be muscular, and proceeds to state that " this muscle has a tendinous centre round the optic nerve, at which part it is attached to the scle rotic coat; the muscular fibres are short, and go off from the central tendon in all directions: the shape of the muscle is nearly that of a horse-shoe; anteriorly it is attached to the choroid coat, and by means of that to the sclerotic. Its action tends evidently to bring the retina forwards ; and in general the optic nerve in fishes makes a bend where it enters the eye, to admit of this motion without the nerve being stretched. In those fishes that have the sclerotic coat completely covered with bone, the whole adjustment to great dis tances must be produced by the action of the choroid muscle; but in the others, which are by far the greater number, this effect will be much assisted by the action of the straight muscles pulling the eye-ball against the socket, and compressing the posterior part, which, as it is the only membranous part in many fishes, would appear to be formed so for that pur pose." Although it must be admitted that these conclusions of Sir E. Home are derived from insufficient data, and are probably incor rect in many particulars, yet it is not very im probable that the part in question may be mus cular, and, if so, may be instrumental in adapt ing the eye to distance by pushing up the retina toward the lens. The organization of
the part is certainly not merely vascular, as stated by Cuvier, and undoubtedly bears a stronger resemblance to muscular than any other structure; it also retains the peculiar colour of red muscle after all the rest of the eye has been blanched by continued macera Lion in water. I think, however, Sir E. Home goes too far when he describes a central tendon without reservation.
For further information on the subject of this article, see Vlstox, and VISION, ORGAN OF.
FACE (in anatomy) (Gr. nog-armor ; Lat. fades, mates, os ; Fr..face ; Germ. Anaitz, Goleta ; Ital.joecia).—In vertebrated animals this term is applied to denote the anterior part of the head, with which most of the organs of the senses are connected ; while the cranium is destined to contain and protect the encephalic organs, the face is the scat of the organs of sight, smell, and taste, and in some animals of a special organ of touch. The relative sizes of cranium and face depend, therefore, in a great measure on the relative development of those important organs which belong to each. For the characters of the face in the different classes of animals, we refer to the articles devoted to the anatomy of them, and to the article OSSEOUS SYSTEM.
FACE (in human anatomy). The face is situated before and below the cranium, which bounds it above ; on the sides, it is limited by the zygomatic arches, behind by the cars and the depression which corresponds to the upper region of the pharynx, and below by the base of the lower jaw and the chin. The disposition of the face is symmetrical ; its anterior surface is trapezoidal, the largest side being above ; and its vertical section is triangular. It pre sents an assemblage of organs which serve dif ferent purposes, and which by their configura tion and proportions constitute what are tailed the features ; individually the face presents many varieties, not only in the (Cain and degree of development of its several parts, as the nose, mouth, &c., but also in the condition of its bones, muscles, skin, and adipose tissue. The varieties of form presented by the face afliard sonic of the most distinctive characters of the different races of mankind. It differs also ac cording to the age and sex of the individual ; in the infant, the peculiarities depend princi pally upon the disposition of the bones, and in particular on the absence of the teeth ; but the soft parts have also their distinctions at this age, for while the fat is abundant, the muscles are but little developed, and hence the slightly marked features and the plump cheeks of infancy.
In old age, again, the aspect of the face is the reverse of this, for not only do its thinness and the predominance of the muscles throw out the features, but the skin is covered with folds and wrinkles, from its own relaxation and the absence of fat, aided perhaps by the action of the muscles. The loss of the teeth, moreover, allows the lower jaw (when the mouth is closed) to be thrown in front of the upper, and thus the length of the face is dimi nished, and a peculiar expression is imparted to tine countenance.
In women, (from the delicacy of the features and the abundance of the cellular tissue,) the face preserves the roundness of form, and something of the characteristics of childhood.