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The deep fascia of the head and neck presents many remarkable characters. Over the scalp it is represented by the galea aponeurotica (O.T. epicranial aponeurosis), the tendon of the epicraneus muscle. This is a tough membrane, tightly stretched over the calvaria, from which it is separated by loose areolar tissue. It is attached posteriorly, partly through the agency of the occipitalis muscle, to the superior nuchal line of the occipital bone; anteriorly it joins the frontalis muscle and the orbicularis oculi, and has no bony attachment; laterally it is attached to the temporal line and the mastoid process. Below the temporal line it is continuous with the temporal fascia, a stout layer of fascia attached to the temporal line and zygomatic arch, which covers and gives origin to the temporal muscle. This fascia separates into two layers above the zygomatic arch, to enclose a quantity of fat along with branches of the temporal and zygomatico-orbital arteries. On the face the fascia is practically non-existent anteriorly in relation to the facial muscles. Posteriorly it forms the thin parotideo masseteric fascia, and is much thicker in relation to the parotid gland, for which it forms a capsule.
In the neck the deep
9. Layers of deep cervical fascia.
13. Cervical fascia.
17. STERNO-MASTOID MUSCLE.
19. Vagus nerve.
21. Carotid sheath.
22. Phrenic nerve.
23. LONGUS COLLI MUSCLE.
24. LONGUS CAPITIS.
vessels. It encloses the
7. Thyreoid cartilage.
1. CRICO-ARYTENOIDEUS POSTERIOR
2. INFERIOR CONSTRICTOR MUSCLE.
4. Cricoid cartilage.
5. Vocal fold.
6. VOCALIS AND THYREOARYTENOIDEUS
FIG. 397.-TRANSVERSE SECTION IN THE CERVICAL REGION
26. Vertebral vein.
31. Accessory nerve.
32. SPLENIUS CERVICIS.
37. Profunda cervicis vein.
40. SEMISPINALIS CERVICIS.
41. SEMISPINALIS CAPITIS
42. SPLENIUS CAPITIS.
44. Ligamentum nucha.
45. Spine of fourth cervical vertebra.
46. Lamina of fifth cervical vertebra.
47. Dura mater.
48. Spinal medulla.
49. Transverse process.
50. Fibrocartilage between fourth and
fifth cervical vertebræ.
œsophagus, and pharynx, and the prævertebral muscles. The trachea, esophagus, and pharynx are likewise encapsuled in cervical fascia, a septal layer passing across the median plane of the neck between the trachea and oesophagus. Lastly, a strong prævertebral fascia passes across the neck anterior to the prævertebral muscles, and posterior to the œsophagus and pharynx.
The cervical fascia is attached above to the bones of the skull: superficially to the superior nuchal line of the occipital bone, the mastoid process, the zygoma (over the parotid gland), and the inferior border of the mandible; more deeply to the styloid and vaginal processes of the temporal bone, the great wing of the sphenoid and the basilar part of the occipital bone. This deeper attachment (prævertebral fascia) is posterior to the parotid gland and pharynx, and is associated with the formation of three ligaments: stylo-mandibular ligament, sphenomandibular ligament, and pterygo-spinous ligament. The fascia is attached below, through its muscular connexions, to the sternum, first rib, clavicle, and scapula. By means of its connexion with the trachea and the common carotid artery it is carried down behind the first rib into the superior mediastinum, and so becomes continuous with the pericardium. By means of its connexion with the subclavian vessels and brachial nerves it is carried down to the axilla, as the axillary sheath, which becomes connected with the costo-coracoid membrane.
THE MUSCLES OF THE HEAD.
The muscles of the head are divisible into three separate groups: the superficial muscles, muscles of the orbit, and muscles of mastication.
The superficial muscles comprise a large group, including the muscles of the scalp and face, and the platysma in the neck.
The platysma is a thin quadrilateral sheet extending from chest to face over the side of the neck, between the superficial and deep fasciæ. It arises from the deep fascia of the pectoral region.
It is directed upwards and forwards, and is partly inserted (by its intermediate fibres) into the inferior border of the mandible, becoming connected with the quadratus labii inferioris and triangularis muscles (Fig. 398, p. 449). The more anterior fibres pass across the median plane of the neck and decussate for a variable distance below the chin with those of the opposite side. The posterior fibres sweep over the angle of the jaw and become continuous with the risorius muscle. The platysma is the rudiment of the cervical portion of the panniculus carnosus of lower animals, in which it has a much more intimate connexion with the muscles of the face than is usually the case in man.
Nerve-Supply.-Cervical branch of the facial nerve.
Actions. It depresses the mandible and laterally flexes the head. It also throws into folds the skin of the side of the neck.
The Muscles of the Scalp.
The muscles of the scalp comprise the epicranius muscle and the muscles of the auricle.
M. Epicranius.-The epicranius (O.T. occipitofrontalis) is a muscle with four bellies, two posterior and two anterior, and an intervening tendon (the galea aponeurotica) which stretches uninterruptedly across the median plane of the cranium. Each posterior belly (occipitalis) arises as a broad flat band from the lateral two-thirds of the superior nuchal line of the occipital bone. Each anterior belly (frontalis) has no bony attachments; arising from the galea aponeurotica about the level of the coronal suture, it passes downwards to the supra-orbital arch, where it blends with the orbicularis oculi and corrugator supercilii muscles. It extends across the full width of the forehead, and blends in the median plane with the muscle of the opposite side.
The galea aponeurotica (O.T. epicranial aponeurosis), extending between the two anterior and the two posterior fleshy bellies, is a continuous membrane which glides over the calvaria, and has attachments laterally to the temporal ridge, and behind, between the posterior bellies, to the superior nuchal lines of the occipital bone. It has no osseous attachment anteriorly.
Nerve-Supply.-The occipitalis is supplied by the posterior auricular branch of the facial nerve. The frontalis is supplied by the temporal branches of the same nerve.
Actions. The epicraneus is usually rudimentary. By the contraction of the fibres of the frontalis muscle the skin of the forehead is thrown into horizontal parallel folds.
FIG. 398.-THE MUSCLES OF THE FACE AND SCALP (Muscles of Expression).
M. QUADRATUS LABII INFERIORIS
The extrinsic muscles of the ear are three in number: posterior, superior, and anterior. They are rudimentary and usually functionless.
The m. auricularis posterior (O.T. retrahens aurem) is a narrow fleshy slip which arises from the surface of the mastoid process and is inserted into the cranial surface of the auricle. It bridges across the groove between the mastoid process and the auricle, and conceals the posterior auricular vessels and nerve.
The m. auricularis superior (O.T. attollens aurem) is a small fan-shaped muscle which arises from the temporal fascia, and descends to be inserted into the top of the root of the auricle.
The m. auricularis anterior (O.T. attrahens aurem) is a similar small muscle, placed in front of the auricularis superior, and stretching obliquely between the temporal fascia and the top of the root of the auricle.
The Muscles of the Face.
The facial muscles are divided into three groups, associated with the several apertures of the eye, nose, and mouth.
1. The muscles of the eyelids include four muscles: the levator palpebræ superioris (described with the orbital muscles (p. 452)), orbicularis oculi, lacrimal part of the orbicularis, and corrugator supercilii.
M. Orbicularis Oculi.-The orbicularis oculi is a transversely oval sphincter muscle surrounding and occupying the eyelids. It is divisible into an orbital portion (pars orbitalis) composed of coarse fibres, spreading on to the forehead, temple. and cheek, and a palpebral portion (pars palpebralis), composed of finer fibres, situated beneath the skin of the eyelids. At the medial commissure of the eye the muscle (by its palpebral fibres) gains an attachment to the medial palpebral ligament and the borders of the naso-lacrimal groove. Its fibres enclose the lacrimal sac and the canaliculi. The posterior fibres, extending between the posterior edge of the naso-lacrimal groove and the tarsal ligaments behind the lacrimal sac, constitute the pars lacrimalis (O.T. tensor tarsi muscle). The fibres of the muscle which extend along the margins of the lids constitute a separate ciliary bundle.
Laterally the orbicularis oculi has no bony attachment; so that when it contracts and closes the eyelids, both lids at the same time tend to be drawn towards the medial commissure of the eye.
M. Corrugator Supercilii.-The corrugator supercilii arises from the medial part of the superciliary arch, and passing horizontally laterally, blends with the upper fibres of the orbicularis oculi on its deep surface. The contraction of this muscle throws the skin of the forehead into vertical folds, while at the same time drawing the medial half of the eyebrow upwards, it produces concentric curved folds on each side of the median plane of the forehead.
2. The muscles of the nose comprise five small muscles proper to the nose, and one common to the nose and upper lip: the m. procerus, nasalis, dilatores naris (anterior and posterior), depressor alæ nasi, and angular head of the quadratus labii superioris. They are all small and feeble muscles.
The m. procerus (O.T. pyramidalis nasi) arises from the epicranius muscle and the skin over the glabella; it is inserted into a membrane stretching over the nose, which gives attachment to the musculus nasalis also.
The m. nasalis (O.T. compressor naris) arises by a narrow origin from the maxilla, under cover of the quadratus. It passes forwards over the bridge of the nose, and ends in a membranous insertion common to it and the preceding muscle.
The mm. dilatores naris are feeble muscular slips placed on the lateral surface of the margin of the nostril, one anteriorly, the other posteriorly.
The m. depressor alæ nasi is a small muscle arising from the upper part of the incisor fossa of the maxilla; it divides into two parts as it passes upwards and medially, and is inserted into the ala and the septum of the nose (depressor septi).
The caput angulare (O.T. levator labii superioris alæque nasi) is a portion of the quadrate muscle of the upper lip, and is a narrow band arising from the root of the frontal process of the maxilla. It descends alongside the nose, and is inserted, partly into the ala of the nose and partly into the orbicularis oris muscle.
3. The muscles of the mouth comprise a number of muscles, of which all but one, the orbicularis oris, are bilaterally placed. The muscles are: (1) quadratus labii superioris, which includes the angular head just described, the infra-orbital head, and the zygomatic head; (2) the canine muscle; (3) zygomaticus; (4) risorius; (5) orbicularis oris; (6) triangularis; (7) quadratus labii inferioris; (8) mentalis; and (9) buccinator.
M. Orbicularis Oris.-The orbicularis oris is the sphincter muscle surrounding the lips. It is continuous with the other muscles converging to the mouth. It lies between the skin and mucous membrane of the mouth, and is limited superiorly by the nose, inferiorly by the junction of the lower lip and chin. Its medial fibres are attached above to the septum of the nose (naso-labial band) and
to the incisor fossa (superior incisive bundle); below they are attached to the mandible on each side of the symphysis (inferior incisive bundle). These bundles radiate laterally to join the rest of the muscle, which is joined at its margin by the elevators and depressors of the lower lip and angle of the mouth, and by the buccinator muscle. The lower fibres of the muscle are continued laterally into the buccinator and canine muscles; its upper fibres are continued into the buccinator and triangularis muscles.
M. Quadratus Labii Superioris.-The quadratus labii superioris comprises three muscles.
(1) The caput angulare (O.T. levator labii superioris alæque nasi) has already been described.
(2) The caput infra-orbitale (O.T. levator labii superioris) arises from the maxilla just above the infra-orbital foramen. It passes almost vertically downwards to join the orbicularis oris and the skin of the upper lip between the attachments of the caput angulare and the caninus. It conceals the infra-orbital vessels and nerve.
(3) The caput zygomaticum (O.T. zygomaticus minor) arises from the zygomatic bone, and is often continuous with the most peripheral fibres of the orbicularis oculi. It is directed obliquely downwards and forwards over the caninus, to be inserted along with the caput infra-orbitale into the margin of the orbicularis oris.
M. Caninus.—The caninus (O.T. levator anguli oris) arises from the canine fossa of the maxilla below the infra-orbital foramen and under cover of the caput zygomaticum. It is directed laterally and downwards, to be inserted into the orbicularis oris and the skin at the angle of the mouth.
M. Zygomaticus.-The zygomaticus (O.T. zygomaticus major) is a narrow muscular band which arises from the zygomatic portion of the zygomatic arch. It passes to the angle of the mouth, to be inserted partly into the skin, partly into the orbicularis oris.
M. Risorius. The risorius is a thin flat muscle which forms in part a continuation of the platysma on the face, in part a separate muscle, with an origin from the parotideo - masseteric fascia. It passes transversely forwards, to be inserted at the angle of the mouth into the orbicularis oris and skin.
M. Triangularis.-The triangularis (O.T. depressor anguli oris) arises from the oblique line of the mandible and is continuous with the platysma (Fig. 398, p. 449). It is triangular in form, its fibres converging to the angle of the mouth, where they are inserted into the orbicularis oris and the skin. Some of the fibres reach the upper lip through the orbicularis muscle.
M. Quadratus Labii Inferioris.-The quadratus labii inferioris (O.T. depressor labii inferioris) arises from the lateral surface of the mandible deep and medial to the preceding muscle (Fig. 398, p. 449). It is quadrilateral in form, and is directed upwards, to be inserted into the orbicularis oris and the skin of the lower lip. Its lateral fibres are overlapped by the triangularis. Its medial fibres join with those of the opposite muscle.
M. Mentalis. The mentalis (O.T. levator menti) is a small muscle which arises from the incisor fossa of the mandible and is inserted into the skin of the chin.
M. Buccinator. The buccinator muscle forms the lateral wall of the mouth, and is in series posteriorly with the constrictor muscles of the pharynx. It arises (1) from the alveolar arches of the maxillæ and mandible (Fig. 407, p. 457), and between these attachments; (2) from the pterygo-mandibular raphe. Its fibres are directed forwards to the angle of the mouth, where they blend with the corresponding (upper and lower) portions of the orbicularis oris muscle. The middle fibres of the muscle decussate at the angle of the mouth, so as to pass, the lower set to the upper lip, the upper set to the lower lip. The buccinator is covered on its deep surface by the mucous membrane of the mouth. Superficially it is concealed by the muscles above mentioned, which converge to the angle of the mouth; it is separated from the masseter by the corpus adiposum bucca; it is pierced by the duct of the parotid gland, and by branches of the buccinator nerve.