talis, assists that muscle in its action; it also draws down the inner angle of the eyebrow, and by its insertion fixes the aponeurosis of the compressores narium, and tends to elevate the nose. The compressores narium appear to act in expanding rather than compressing the nares; hence probably the collapsed state of the nares from paralysis of these muscles in the last moments of life, or in compression of the brain. The dilatator naris is a dilator of the nostril, and the depressor alæ nasi draws downwards both the ala and columna of the nose, the depression of the latter being assisted by the naso-labialis.

5. Superior Labial Group.
Orbicularis oris,

Levator labii superioris alæque nasi,
Levator labii superioris proprius,

Levator anguli oris,

Zygomaticus major,
Zygomaticus minor.

The ORBICULARIS ORIS is a sphincter muscle, completely surrounding the mouth, and possessing consequently neither origin nor insertion. It is composed of two thick semicircular planes of fibres, which embrace the rima of the mouth, and interlace at their extremities, where they are continuous with the fibres of the buccinator, and the other muscles connected with the angle of the mouth. The upper segment is attached by means of a small muscular fasciculus (nasolabialis) to the columna of the nose; and other fasciculi connected with both segments, and attached to the maxillary bones, are termed "accessorii." Several anatomists consider the orbicularis as composed of two portions, internal or marginal, in immediate contact with the lips, and thick; and external, broad and thin; the separation between the two being indicated by the coronary arteries. Relations. By its superficial surface with the integument of the lips, with which it is closely connected. By its deep surface with the mucous membrane of the mouth, the labial glands and coronary arteries being interposed. By its circumference with the numerous muscles which move the lips, and by the inner border with the mucous membrane of the rima of the mouth.

The LEVATOR LABII SUPERIORIS ALÆQUE NASI (pyramidalis) is a thin triangular muscle; it arises from the upper part of the nasal process of the superior maxillary bone; and, becoming broader as it descends, is inserted by two portions, one into the ala of the nose, the other into the orbicularis oris and upper lip.

Relations. By its superficial surface with the orbicularis palpebrarum, facial artery, and integument. By its deep surface with the superior maxillary bone, musculus anomalus, compressor naris, dilatator naris, and alar cartilage.

The LEVATOR LABII SUPERIORIS PROPRIUS (incisorius) is a thin quadrilateral muscle; it arises from the lower border of the orbit, and passing obliquely downwards and inwards, is inserted into the integument of the upper lip, its deep fibres being blended with those of the orbicularis.

Relations. By its superficial surface with the lower segment of the orbicularis palpebrarum, facial artery, and integument. By its deep surface with the compressor naris, levator anguli oris, orbicularis oris, and infraorbital artery and

nerve.

The LEVATOR ANGULI ORIS (caninus) arises from the canine fossa of the superior maxillary bone, and passes obliquely outwards to be inserted into the angle of the mouth; its fibres being continued into the inferior segment of the orbicularis, and depressor anguli oris.

Relations. By its superficial surface with the levator labii superioris proprius, branches of the infraorbital artery and nerve, and inferiorly with the integument. By its deep surface with the superior maxillary bone and buccinator muscle.

The ZYGOMATIC muscles are two slender fasciculi of fibres which arise from the malar bone, and are inserted into the upper lip. The zygomaticus major descends to the angle of the mouth, and is continuous with the inferior segment

of the orbicularis, depressor anguli oris, and risorius Santorini. The zygomaticus minor, lying in front of the major, becomes connected with the outer border of the levator labii superioris proprius, and is attached to the integument of the upper lip. This muscle is often wanting.

Relations. The zygomaticus major is in relation by its superficial surface with the lower segment of the orbicularis palpebrarum above, and with the fat of the cheek and integument for the rest of its extent. By its deep surface with the malar bone, masseter and buccinator muscles, and facial vessels. The zygomaticus minor being in front of the major, has no relation with the masseter; inferiorly it rests on the levator anguli oris.

Actions. The orbicularis oris produces the direct closure of the lips by means of its continuity, at the angles of the mouth, with the fibres of the buccinator. When acting singly in the forcible closure of the mouth, the integument is thrown into wrinkles, in consequence of its firm connexion with the surface of the muscle; its naso-labial fasciculus draws downwards the columna nasi. The levator labii superioris alæque nasi lifts the upper lip with the ala of the nose, and expands the opening of the nares. The levator labii superioris proprius is the proper elevator of the upper lip; acting singly, it draws the lip a little to one side. The levator anguli oris lifts the angle of the mouth and draws it inwards, while the zygomatici pull it upwards and outwards, as in laughing, and prodnce the dimple in the cheek. In the movement of laughter the zygomatici are assisted by the risorius Santorini.

6. Inferior Labial Group.

[Orbicularis oris,]
Depressor labii inferioris,
Depressor anguli oris,

Risorius Santorini,
Levator labii inferioris.

Dissection. To dissect the inferior labial region, continue the vertical section from the middle of the lower lip to the point of the chin. Then carry an incision along the margin of the lower jaw to its angle. Dissect off the integument and superficial fascia from this surface, and the muscles of the inferior labial region will be exposed

[The Orbicularis oris. This muscle has been described with the previous group.]

The DEPRESSOR LABII INFERIORIS (quadratus menti) arises from the oblique line by the side of the symphysis of the lower jaw, and passing upwards and inwards, is inserted into the orbicularis muscle and integument of the lower lip. Its inner fibres interlace with those of the opposite muscle, the outer fibres reach nearly to the angle of the mouth.

Relations. By its superficial surface with the platysma myoides, part of the depressor anguli oris, and the integument of the chin with which it is closely connected. By the deep surface with the levator labii inferioris, labial glands, mucous membrane of the lower lip, and mental nerve and artery.

The DEPRESSOR ANGULI ORIS (triangularis) is a triangular plane of muscle arising by a broad base from the external oblique ridge of the lower jaw, and inserted by its apex into the angle of the mouth, where it is continuous with the levator anguli oris, zygomaticus major, and upper segment of the orbicularis Near its insertion it is joined by the following muscle.

Relations. By its superficial surface with the integument; by its deep surface with the depressor labii inferioris, buccinator, and branches of the mental nerve and artery.

The RISORIUS SANTORINI is a thin and triangular muscle, consisting of a few scattered fasciculi of fibres which arise from the fascia, covering the masseter muscle, and converge to the angle of the mouth, where they become connected with the outer border of the depressor anguli oris, and continuous with the

zygomaticus major. This muscle is generally regarded as a part of the platysma myoides.

The LEVATOR LABII INFERIORIS (levator menti) is a short but strong muscle arising from the incisive fossa of the lower jaw, and inserted into the integument of the chin. It is in relation with the mucous membrane of the mouth, with its fellow, and with the depressor labii inferioris.

Actions. The depressor labii inferioris draws the lower lip directly downwards, and at the same time a little outwards. The depressor anguli oris, from the radiated direction of its fibres, will pull the angle of the mouth either downwards and forwards, or downwards and backwards, and be expressive of grief; or acting with the levator anguli oris, zygomaticus major, and risorius Santorini, will draw the angle of the mouth upwards and backwards, or directly backwards. The levator labii inferioris raises and protrudes the integument of the chin.

7. Maxillary Group.

Masseter,
Temporalis,

Buccinator,
Pterygoideus externus,
Pterygoideus interuus.

Dissection. The masseter has been already exposed by the preceding dissec

tion.

-

The MASSETER (μassaoua, to chew,) is a short, thick, and somewhat quadrilateral muscle, composed of two planes of fibres, superficial and deep. The superficial layer arises by a strong aponeurosis from the malar process of the superior maxillary bone, lower border of the malar bone and zygoma; and passes downwards and backwards to be inserted into the ramus and angle of the inferior maxilla. The deep layer arises also from the zygomatic arch but extends further back upon the zygoma, and passes downwards and forwards, to be inserted into the upper half of the ramus. This muscle is tendinous and muscular in structure; and covered in by a fascia (fascia parotideo-masseterica) which is connected with the zygomatic arch above, and incloses the parotid gland behind.

Relations. By its external surface with the zygomaticus major, risorius Santorini and platysma myoides, parotid gland and Stenon's duct, transverse facial artery, pes anserinus, and integument. By its internal surface with the temporal muscle, buccinator, from which it is separated by a mass of fat, and ramus of the lower jaw. By its posterior border with the parotid gland; by the anterior border with the facial artery and vein.

Dissection. Make an incision along the upper border of the zygoma, for the purpose of separating the temporal fascia from its attachment. Then saw through the zygomatic process of the malar bone, and through the root of the zygoma near the meatus auditorius. Draw down the zygoma, and with it the origin of the masseter, and dissect the latter muscle away from the ramus and angle of the inferior maxilla. Now remove the temporal fascia from the rest of its attachment, and the whole of the temporal muscle will be brought into view.

The TEMPORALIS (crotaphytes) [xpórapos, the temple], is a broad and radiating muscle, occupying a considerable extent of the side of the head, and filling the temporal fossa. It is covered in by a dense fascia (temporal fascia), which is attached along the temporal ridge on the side of the skull, extending from the external angular process of the frontal bone to the mastoid portion of the temporal; and inferiorly to the upper border of the zygoma. The muscle arises by tendinous fibres from the whole length of the temporal ridge, and by muscular fibres from the temporal fascia and entire surface of the temporal fossa. Its fibres converge to a strong and narrow tendon, which is inserted into the apex and internal surface of the coronoid process of the lower jaw.

Relations. By its external surface with the temporal fascia (which separates

it from the attollens and attrahens aurem muscle, and temporal vessels and nerves) and with the zygoma and masseter. By its internal surface with the bones forming the temporal fossa, the external pterygoid muscle, part of the buccinator, and the internal maxillary artery with its deep temporal branches.

By sawing through the coronoid process near its base, and pulling it upwards, together with the temporal muscle, which may be dissected from the fossa, we obtain a view of the entire extent of the buccinator and external pterygoid muscle.

The BUCCINATOR (buccina, a trumpet; alveolo-labialis), the trumpeter's muscle, arises from the alveolar process of the superior maxillary bone, the external oblique line of the inferior maxillary as far forwards as the second bicuspid tooth, and the pterygo-maxillary ligament. This ligament is the raphé of union between the buccinator and superior constrictor muscle, and is attached by one extremity to the hamular process of the internal pterygoid plate, and by the other to the extremity of the molar [or mylo-hyoidean] ridge. The fibres of the muscle converge towards the angle of the mouth, where some are continuous with the levator and depressor anguli oris, and the rest cross each other, the superior being continuous with the inferior segment of the orbicularis oris, the inferior with the superior segment. The muscle is invested externally by a thin fascia (buccal) which extends backwards to the pharynx.

Relations. By its external surface, posteriorly, with a large and rounded mass of fat, which separates the muscle from the ramus of the lower jaw, temporalis, and masseter: anteriorly with the risorius Santorini, zygomatici, levator anguli oris, and depressor anguli oris. It is also in relation with a part of Stenon's duct, (which pierces it opposite the second molar tooth of the upper jaw,) with the transverse facial artery, branches of the facial and buccal nerve, and facial artery and vein. By its internal surface with the buccal glands and mucous membrane of the mouth.

The PTERYGOIDEUS EXTERNUS is a short and thick muscle, broader at its origin than at its insertion. It arises by two heads, one from the under surface of the great ala of the sphenoid, and pterygoid ridge; the other from the external pterygoid plate, tuberosity of the palate bone and tuberosity of the superior maxillary The fibres pass backwards to be inserted into the neck of the lower jaw

FIG. 160.

THE TWO PTERYGOID MUSCLES. The zygomatic arch and the greater part of the ramus of the lower jaw have been re

moved, in order to bring these muscles

into view. 1. The sphenoid origin of

the external pterygoid. 2. Its pterygoid origin. 3. The internal pterygoid.

and into the interarticular fibro-cartilage. The internal maxillary artery passes between the two heads of this muscle.

Relations. By its external surface with the ramus of the lower jaw, temporal muscle, and internal maxillary artery; by its internal surface with the internal pterygoid muscle, internal lateral ligament of the jaw, arteria meningea media, and inferior maxillary nerve; by its upper border with the muscular branches of the inferior maxillary nerve; the internal maxillary artery passes between its two heads, and its lower head is pierced by the buccal nerve.

The external pterygoid muscle must now be removed, the ramus of the lower jaw sawn through its lower third, and the head of the bone dislocated from its socket and withdrawn, for the purpose of seeing the pterygoideus internus.

The PTERYGOIDEUS INTERNUS is a thick quadrangular muscle. It arises from the pterygoid fossa and descends obliquely backwards, to be inserted into the ramus and angle of the lower jaw: it resem

bies the masseter in appearance and direction, and was named by Winslow, internal masseter.

Relations. By its external surface with the external pterygoid, inferior maxillary nerve and branches, internal maxillary artery and branches, internal lateral ligament, and ramus of the lower jaw. By its internal surface with the tensor palati, superior constrictor and fascia of the pharynx; by its posterior border with the parotid gland.

Actions. The maxillary muscles are the active agents in mastication, and form an apparatus admirably fitted for that office. The buccinator circumscribes the cavity of the mouth, and with the aid of the tongue keeps the food under the immediate pressure of the teeth. By means of its connexion with the superior constrictor, it shortens the cavity of the pharynx from before backwards, and becomes an auxiliary in deglutition. The temporal, the masseter, and the internal pterygoid are the bruising muscles, drawing the lower jaw against the upper with great force. The two latter, from the obliquity of their direction, assist the external pterygoid in grinding the food, by carrying the lower jaw forwards upon the upper; the jaw being brought back again by the deep portion of the masseter and posterior fibres of the temporal. The whole of these muscles, acting in succession, produce a rotatory movement of the teeth upon each other, which, with the direct action of the lower jaw against the upper, effects the mastication of the food.

8. Auricular Group.

Attollens aurem,

Attrahens aurem,

Retrahens aurem.

[These three muscles are the extrinsic muscles of the ear. The intrinsic muscles are described with the anatomy of the ear.]'

Dissection. The three small muscles of the ear may be exposed by removing a square of integument from around the auricula. This operation must be performed with care, otherwise the muscles, which are extremely thin, will be raised with the superficial fascia. They are best dissected by commencing with their tendons, and thence proceeding in the course of their radiating fibres.

The ATTOLLENS AUREM (superior auricula), the largest of the three, is a thin triangular plane of muscular fibres, arising from the lateral portion of the galea aponeurotica and aponeurosis of the occipito-frontalis, at about the middle of the temporal ridge, and inserted into the convexity of the fossa triangularis of the pinna.

It is in relation by its external surface with the integument, and by the internal with the galea aponeurotica and temporal fascia.

The ATTRAHENS AUREM (anterior auricula), also triangular, arises from the the lateral portion of the aponeurosis of the occipito-frontalis above the zygoma, and is inserted into the spine of the helix.

It is in relation by its external surface with the integument; and by the internal with the galea aponeurotica, temporal fascia, and temporal artery and

veins.

The RETRAHENS AUREM (posterior auricula), arises by two, (sometimes three). muscular slips from the root of the mastoid process. They are inserted into the posterior surface of the concha.

It is in relation by its external surface with the integument, and by its internal surface with the mastoid portion of the temporal bone.

Actions. The actions of the auricular muscles are expressed in their names; they have but little power in man, but are important muscles in brutes.

[The extrinsic muscles move the auricle as a whole; the intrinsic muscles move the different parts of the auricle upon each other.]