TIIE MUSCLES OF TILE FACE are arranged around the orifices of the eyelids, the nose, and the mouth, and may be divided into constrictors and dilators of these apertures. The nostrils, however, undergo but little vari ation in their dimensions, being maintained permanently open by the elastic cartilages which form them. The eyelids also contain elastic cartilages, which are moulded upon the front of the globe over which they glide in obedience to the muscles which dilate or con tract the orifice between them. The mouth, which is the most mobile of the facial aper tures, is also furnished with its contractor or sphincter muscle, and with many dilators which radiate from it at various angles.
All the muscles of the face are superficially situated, and most of them are subcutaneous.
In the palpebral regions, or about the eye lids on each side, are placed, 1. a constrictor, or the orbicularis palpebrarum, of which the corrugutor supercilii is an associate ; 2. the levator palpcbret and the which are dilators, and antagonists of the two former muscles.
The orbicularispalpebrarum,(naso-palpebral, Chauss.) is a flat oval muscle, situated im mediately underneath the skin, to which it adheres, and covering the base of the orbit and the superficial surface of the eyelids ; in the middle it presents a transverse aperture, which is the orifice of the palpebrx, varying in size according to the individual, and giving apparently a greater or less magnitude to the globe itself, which, however, is of nearly uni form dimensions in different persons. The orbicularis, like the other sphincter muscles, consists of concentric fibres, but it is peculiar in having a fixed tendon on one side, from which a great part of the fibres arise; this tendon the orbicularis, or lipmentum pal pebrx, which is situated horizontally at the inner corner of the eye, is about two and a half lines in length, and half a line in breadth; it arise from the anterior border of the lachry mal groove in the nasal process of the upper maxillary bone, and passing horizontally out wards in front of the lachrymal sac, divides into a superior and an inferior slip, which are attached to the inner extremities of the corres ponding eyelids. The tendon at first is flat
tened anteriorly and posteriorly, but afterwards becomes twisted so as to present horizontal surfaces. From its posterior part is detached a slip of fibres (the reflected tendon of the orbicularis), which proceeds backwards to wards the os unguis, and forms the outer wall of the lachrymal canal.
The orbicularis arises, 1. from the borders and surfaces of this tendon and from its reflected slip ; 2. from the internal angular process of the frontal bone and from the fronto maxillary suture ; 3. from the nasal process of the upper maxillary bone ; and, 4. by short tendinous slips from the inner tbird of the lower border of the orbit. From these origins the upper and lower fibres of the muscle take a curved direction outwards, their concavity look ing towards the aperture of the lids, and fol lowing the course of the upper and lower borders of the orbit, which they overlap. They unite at the outer side; not, however, by a tendinous raphe or septum, as some have described, but simply by the mingling of their fibres. Each half (the upper and lower) of the orbicularis consists really of two sets of fibres; one, which covers the margins of the orbits, and forms the circumference of the muscles, is strong, tense, and of the usual reddish colour ; it arises from the direct ten don, and from the frontal or upper maxillary bone. These form the orbicularis properly so called. The other set, which is pale and thin, covers the lids and proceeds almost in a hori zontal direction outwards from the palpebral bifurcation of the orbicular tendon: this forms the ciliary or palpebrales. These two sets of fibres, as we shall presently see, are distin guished as much by their functions as by their appearance.