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DISSECTION OF THE FACE.

ing bones. They are named elevators, depressors, sphincters, etc., according to their respective action.

Musculus Risorius (Santorini).

This muscle is usually considered as a part of the platysma myoides, the large subcutaneous muscle of the neck. It arises by thin fasciculi from the fascia over the masseter muscle, and passes horizontally forwards to be inserted into the angle of the mouth, where it intermingles with the orbicularis oris and depressor anguli oris. It produces the smile, not of good-humour, but of derision.

This muscle, nearly an inch in breadth, surOrbicularis Oris. rounds the mouth, forming a kind of sphincter. Its size and thickness in different individuals produce the variety in the prominence of the lips. Observe that its fibres, except the most internal, do not surround the mouth in one unbroken series, but that those of the upper and lower lip decussate at the angles of the mouth, and intermingle with the fibres of the buccinator and other muscles which converge from different parts of the face.

The orbicularis consists of two parts, an inner or labial part, and an outer or facial; the difference in appearance of the fibres being very marked. The labial part consists of pale, thin fibres, forming more or less of the inner part of the orbicularis, and has no attachment to bone; the facial part is thinner but broader, and besides being connected with other muscles, is attached to bone thus: in the upper lip by two fasciculi on each side, one to the septum nasi, the other to the alveolar border opposite the incisor teeth; in the lower lip by a single fasciculus to the lower jaw on each side opposite the canine tooth. The cutaneous surface of the muscle is intimately connected with the lips and the surrounding skin; the deep surface is separated from the mucous membrane by the labial glands and the coronary vessels.

The orbicularis is the antagonist of all the muscles which move the lips. Upon a nice balance of their opposite actions depends the play and infinitely varied expression of the mouth.*

Depressor Anguli

Oris.

This muscle arises broadly from the oblique line of the lower jaw behind the foramen mentale, and is inserted narrowly into the angle of the mouth, intermingling with the zygomatici, the risorius, and orbicularis oris. It is an important muscle in the expression of sorrowful emotions. We see its action when children cry.

* In strong muscular lips the upper part of the orbicularis sends a small subcutaneous slip of muscle from each side along the septum nasi nearly to the apex. The interval between the two slips corresponds to the furrow which leads from the nose to the lip. This is the naso-labialis or depressor septi narium of Haller and Albinus.

Depressor Labii Inferioris, or Quad

ratus Menti.

FIG. 14.

This muscle arises from the oblique line of the lower jaw below the foramen mentale, and is inserted into the lower lip, its fibres intermingling with those of its fellow of the opposite It covers the vessels and nerves which

side and the orbicularis. emerge from the foramen.

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Levator Menti, or
Levator Labii
Inferioris.

MUSCLES OF THE FACE.

This muscle arises from the lower jaw, from the fossa below the incisor teeth, and, passing down, is inserted into the skin of the chin. To see it, evert the lower lip and remove the mucous membrane on either side of the frænum. There are two of them, one for each side. Their action is well seen when we shave the chin, or protude the lower lip.

Zygomaticus Major and Minor.

The zygomaticus major arises from the outer surface of the malar bone close to its suture with the zygoma, passes obliquely downwards and inwards, and is inserted into the angle of the mouth, joining the depressor anguli and orbicularis oris.

The zygomaticus minor arises from the outer surface of the malar bone, in front of the preceding, and is inserted into the outer border of the levator labii superioris near the corner of the mouth. The zygomaticus minor is often absent. The zygomaticus major is the muscle of laughing: the minor expresses sadness.

Before examining the orbicularis palpebrarum, notice the tendo oculi. To make the tendon more apparent, the tarsal cartilages should be drawn outward.

This tendon is a thin cord about 4 mm. Tendo Oculi or Palpebrarum. (in.) in length, and is readily felt at the inner angle of the eye by drawing the eyelids outwards. It is fixed to the nasal process of the superior maxillary bone, in front of the lachrymal groove, is U-shaped, and passes horizontally outwards; one limb is attached to the upper, the other to the lower tarsal cartilage.. The tendon crosses the lachrymal sac a little above the centre, and furnishes a tendinous expansion which covers the sac and is attached to the margin of the bony groove which contains it. To see this expansion we must reflect that portion of the orbicularis palpebrarum which covers the sac.

In puncturing the lachrymal sac the knife is introduced below the tendon, in a direction downwards, outwards, and a little backwards. We have to divide the skin, a few fibres of the orbicularis, and the fibrous expansion from the tendo palpebrarum. The angular artery and vein are situated on the inner side of the incision.

Orbicularis Palpebrarum.

This thin, broad muscle surrounds the margin of the orbit and the eyelids, forming a sphincter. It is attached on the inner side to the tendo palpebrarum, to the nasal process of the superior maxillary bone, to the internal angular process of the frontal bone, and to the lower margin of the orbit. From this attachment the fibres form a series of oval curves, taking a wide sweep, and pass uninterruptedly round the eyelids and orbit.

ORBICULARIS PALPEBRARUM.

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The fibres which belong to the eyelids (orbicularis palpebrarum) are thin and pale, and form, over each eyelid, a series of elliptical curves which meet at the external canthus of the lids, and are loosely attached to the external tarsal ligament. The degree of their curvature becomes less as they approach the margin of the lids, so that some fibres proceed close to the lashes.

This was first pointed out by Riolanus,* and described as the musculus ciliaris.†

The fibres which spread over the orbital margins (orbital portion) are thicker and redder, and mingle, on the forehead, with the occipito-frontalis and corrugator supercilii, on the cheek, with the elevators of the upper lip and nose and the zygomaticus minor.

FIG. 15.-TENDON OF THE ORBICULARIS PALPEBRARUM, SHOWING THE UNION OF THIS TENDON WITH THE LACHRYMAL SAC AND THE LACHRYMAL CANALS. (Sappey.)

1. Lachrymal canals. 2, 2. Commencement of these canals in the lids. 3, 3. Internal extremity of the tarsal cartilages. 4, 4. Free border of the lids. 5. Lachrymal sac. 6 Attachment of the tendo oculi to the nasal process of the superior maxillary. 7. The division of the tendo oculi into its two branches. 8, 8. The two branches ensheathing the two lachrymal canals and attached to the internal extremity of the tarsal cartilages.

No fat is found on the eyelids; nothing intervenes between the skin and the muscles but loose connective tissue, that there may be no impediment to the free play of the lids.

The orbicular muscle not only closes the eyelids but protects the eye. When the eye is threatened, the muscle suddenly contracts, presses the eye back into the orbit, and contracts the skin of the

* Anthropologia, lib. v., cap. 10.

Strictly speaking, the musculus ciliaris arises from the two little divisions of the tendo oculi, and is inserted at the external canthus, into the fibrous tissue which unites the two tarsal cartilages.

brow and cheek so as to form a soft cushion in front of it. The cushion itself may be severely bruised, as is seen in a "black eye; but the globe itself is rarely injured. When the eye is closed, as in winking, the palpebral portion of the muscle contracts. Observe this movement, and notice that the lids are drawn slightly inwards as well as closed. The object of this inward motion is to direct the tears towards the inner angle of the eyelids, where they are absorbed by the puncta lachrymalia.

The tensor tarsi muscle is described in the dissection of the orbit.

Since the orbicular muscle is supplied by the facial nerve, it is affected in facial palsy, and the patient cannot close the lids.

Corrugator Supercilii.

This arises from the inner end of the superciliary ridge of the frontal bone, and is inserted into the under surface of the orbicularis palpebrarum and occipito-frontalis. It lies concealed beneath these two muscles, and is the proper muscle of frowning. Its nerve is derived from the facial.

The present being a good opportunity to examine the appendages (tutamina oculi) of the eyes, postpone for the present the dissection of the remaining muscles of the face.

The

The eyelids are two moveable elliptical folds The Eyelids. consisting of strata of different tissues. upper lid is large and more moveable than the lower, so that when the eye is closed, it is mainly by this fold. The interval between the two lids is called the fissura palpebrarum, which terminates on the inner and outer sides in two angles, the canthi. The lids are thickest at their borders, are somewhat curved, and near the inner canthus each presents a slight elevation, the papilla lachrymalis, at the top of which is a small opening, the punctum lachrymale; this is the commencement of a small canal, canaliculus, which receives the tears and conveys them to the lachrymal sac, and thence through the nasal duct to the nose. the inner canthus the two lids are separated by an oval space, the lacus lachrymalis, where the mucous membrane is raised into a rounded eminence, the caruncula.

Caruncula
Lachrymalis.

At

The caruncula lachrymalis is the red rounded eminence situated at the inner canthus and formed by the conjunctiva. It is composed of an aggregation of sebaceous and sweat glands covered by mucous membrane; on the surface of it are minute hairs.

Resting upon the eyeball external to the caruncle is a slight vertical triangular fold of conjunctiva, plica semilunaris, which is the rudimentary membrana nictitans (the third eyelid found in birds). Both in the caruncle and plica semilunaris unstriped muscular tissue has been demonstrated.