Practical Applications

To close the mouth and draw the jaw forward. Syner- gists: Temporals and pterygoids. Antagonists: The same that antagonize the temporal muscle. Nerve-supply: The masseteric branch of the inferior maxillary division of the trigeminus, Its nerve passes through the sigmoid notch of the ramus with the masseteric vessels. Blood-supply : The muscular branches of the second stage of the internal maxillary artery. The External Pterygoid Muscle. Heals: (1) Upper; (2) lower. Origin of upper head The greater wing of the sphenoid, internal to the pterygoid ridge, and external to the foramen ovale and foramen spinosum. Origin of lower head : The outer surface of the external pterygoid plate. Insertion of upper head: The interarticular fibrocartilage, the capsule of the joint, and neck of the condyle. Insertion of lower head: The neck of the condyle. Action: To draw the condyle and interarticular fibrocartilage forward and inward. Synergists: Superticial layer of masseter and internal pterygoid. Antagonists: The temporal and deep layers of the masseter. Nerve-supply: The pterygoid branch of the inferior -_ _ | THE FACE. 31 maxillary division of the trigeminus. Blood-supply: The second stage of the internal maxillary artery. The Internal Pterygoid Muscle. Oriyin: (1) The inner surface of the external pterygoid plate ; (2) the tuberosity of the palate and adjacent part of the maxilla. Insertion: The internal surface of the ramus, as high as the mandibular foramen Fie. 1. EXTERNAL. PTERYGOID TEMPORAL MANDIBULAR, CANAL INTERNAL, PTERYGOID ‘TEMPORAL CORONOID_ Process MASSETER ANGLE Figs. 11 and 12 show attachments of the muscles of mastication to the mandible. (Montimen FRANK ) and mylohyoid grgove. Action: To close the mouth and draw jaw forward and to the opposite side. Synergists : The temporal and masseter muscles. Antagonists : The digastric and platysma. Nerve-supply: The inferior maxillary division of the trigeminus. Blood-supply: The second stage of the internal maxillary artery. 32 A MANUAL OF DISSECTION. The Buccinator arises from: (1) The pterygomaxillary ligament; (2) the alve- olar process of the upper jaw; (8) the alveolar process of the lower jaw. It is inserted into the orbicularis oris in this manner: The upper and lower fibres con- verge toward the angle of the mouth, where they decussate to become continuous with the fibres of the orbicularis oris. The highest and lowest fibres do not decus- sate. The buccinator and superior constrictor of the pharynx are united by the pterygomaxillary ligament forming a continuous muscular wall for the mouth and pharynx. The ligament extends from the hamular process to the posterior extremity of the mylohyoid ridge near the wisdom tooth. The principal use of the ligament, then, is to form a common attachment for the superior constrictors of the pharynx and buccinator. The buccinator muscle expels air from the mouth, widens the mouth, and assists the tongue in keeping the food between the molar teeth during mastication. Nerve-supply: The fifth and seventh cranial nerves, The Buccinator Fascia takes its name, according to a general rule, from the muscle which it invests and strengthens. This fascia adheres closely to the outer wall of the muscle, and must be removed to appreciate the direction of its fibres. It is thin in front and dense behind, where it is then continuous with the aponeu- rosis of the pharynx, and consequently strengthens the junctional area between the mouth and pharynx ; for this reason it is called the buccopharyngeal fascia. Owing to the strength of this fascia, and to the great vitality of the buccinator and superior constrictor muscles of the pharynx, abscesses do not readily break into the mouth and pharynx. TABLE OF MuscLEs oF MasTIcaTION. Name. Origin, Insertion. Action, Paralytie symptoms, Maseeter. Malar process of Angle and lower To draw jnw for- Lessened ability to pro- superior max.; one-half of outer ward and up- trade chin. anterior two. | surface of ramus, ward. thirds lower bor- der zygomatic arch. Inner surface zygo- Outer surface of To draw jaw up Lessened ability to retract matic arch; post. upper half of and back. and elevate jaw. one-third of ramus and coro- lower border. noid process. Temporal. Temporal ridge Coronoid process. Ant. half elevates Partial loss of power to ‘and fossa. the jaw; post. elevate and retract jaw. half retracts and elevates jaw. External Als of aphenoid. Interarticular car- To draw cartilage A peculiar creaking noise pterygoid. tilage. inward and for- produced by the con- ward onto the dyle riding over the eminentia articu- stationary fibrocartilage ; laris. noise both subjective and objective symptom. Outer surface of Neck of condyle. To draw jaw for- Inability to move jaw external ptery- ward and in- toward the affected side ; goid plate. ward. when chin is depressed deviation of jaw to paralyzed side (Ciowere). Internal Inner surface of Inner surface of To draw jaw for- Inability to draw closed pterygoid. external ptery- lower half of ward, upward, jaw forward. goid plate; tuber- ramus. and to the oppo- osities of palate site cide. and superior maxilla. Buccinator. Outer surfaces of Orbicularis oris. To abduct corners Inability to widen the both upper and f mouth; to mouth ;_ pendulous lower alveolar force food into cheeks during mastica- processes; ptery vestibule. tion gomaxillary ligament, THE FACE. 33 Summary of Nerve-supply. The buccinator receives a motor branch from the seventh and a sensory from the fifth nerve. The remaining muscles are innervated by the inferior maxillary division of the fifth nerve. Masseter. The nerve to the masseter passes outward above the external ptery- goid muscle with the masseteric vessels, through the sigmoid notch of the ramus, and enters the inner surface of the muscle. Temporal. There are interior and posterior deep temporal nerves, probably cor- responding to like physiolo ical portions of the muscle which they supply. They pass over the upper border of the external pterygoid muscle, to the temporal muscle, and bone. External Pterygoid. The branch to this muscle is from the long buccal nerve. Fra. 18. : POSTERIOR TEMPORAL, Auricucan TEMPORAL BRANCH BRANCHES To. OF BuccaL -INFRAORBITAL ~LONG BuccaL AURICULO- temponat YG MyLonyorn LINGUAL Mandibular division of the trifacial nerve. (Geis after TestvT.) Internal Pterygoid. The nerve to this muscle is distributed to the inner surface of the muscle. e The Buccinator. The long buccal nerve passes between the upper and lower heads of the external pterygoid, with the buccal artery, and subsequently under cover of the temporal and masseter muscles to the buccinator muscle, and divides into the sensory branches for the skin and cheek. This muscle derives its motor branches from the seventh nerve. The muscles of mastication derive their blood- supply from the second or pterygoid stage of the internal maxillary artery. Col- lectively, branches of both the artery and nerves are called muscular ; individu- ally, each takes the name of the muscle it supplies. 3 34 A MANUAL OF DISSECTION. TEMPOROMANDIBULAR ARTICULATION. Osteological Elements of the Temporomandibular Region. The tympanic plate is a thin lamina which forms the posterior part of the glenoid fossa and the anterior wall of the middle ear and external auditory meatus. It terminates externally in the auditory process, below in the vaginal process, above in the Glaserian fissure. The Eminentia Articularis is the broad, strong, anterior root of the zygomatic process of the temporal bone. It forms the anterior boundary of the glenoid fossa, and is covered with cartilage. The preglenoid tubercle, at the outer end of the anterior root, is for the attachment of a portion of the external lateral ligament. The Postglenoid Tubercle, or middle root of the zygoma, forms the posterior boun- dary of the articular part of the glenoid fossa, and separates the auditory process from the articular part of the glenoid fossa. The Glaserian or petrotympanic fissure is between the squamous and tympanic clemeuts of the temporal bone It separates the articular from the non-articular part of the glenoid cavity. It leads into the tympanum, lodges the processus gracilis of the malleus, and transmits the tympanic branch of the internal maxil- lary artery to the middle ear. The Canal of Huguier or iter chord anterius is a subdivision of the Glaserian fissure. It transmits the chorda tympani nerve from the tympanum to the zygo- matic fossa, where, after communicating with the otic ganglion, it passes beneath the external pterygoid muscle to the outer side of the lingual nerve. The Glenoid Fossa is situated in a recess between the squamous and tympanic parts of the temporal bone. It is bounded anteriorly by the eminentia articularis, posteriorly by the tympanic plate. The anterior and posterior limiting structures of the glenoid fossa meet at the Glaserian fissure. The glenoid fossa consists of two parts: (1) One anterior to the Glaserian fissure, covered with cartilage and called the mandibular because it articulates with the condyle of the mandible ; (2) another, posterior to the Glaserian fissure, and occupied by a part of the parotid gland. The dome of the glenoid fossa is very thin and easily fractured. The Condylar Process of the mandible consists of (1) a condyle; (2) a neck. The condyle articulates with the articular part of the glenoid cavity. Its convex surface is covered with cartilage. Its transverse axis is greater than its antero- posterior, Its articular surface is surrounded by the origin of the mandibular part of the capsular ligament. The neck is the constricted part of the process below the condyle. It is flattened in front and gives insertion to the external pterygoid muscle. The Styloid Process is, morphologically, not a part of the temporal bone. It was evolved from the dorsal extremity of the second visceral arch and became united to the inferior surface of the petrosa. It gives origin to three muscles and two ligaments, as follows: stylohyoid muscle, from the back and outer surface ; styloglossus muscle, front and lower part of the tip; stylopharyngeus muscle, from internal part of the base ; stylomandibular ligament, from tip of the styloid ; stylohyoid ligament, from tip of styloid. The temporomandibular articulation is held in position or its range of move- ments limited by certain periosteal and fascial ligaments. ne of these, the pos- terior, is always ruptured in dislocation of the jaw. LIGAMENTS OF LOWER JAW. The ligaments are the following: the capsular ¢ anterior part of the capsule ; the posterior part of the capsule ; the ligament ; the external lateral ligament ; the sphenomandibular ligament ; the stylomandibular ligament ; the interarticular fibrocartilage. THE FACE. 35 The Capsular Ligament is loose and flabby, and is attached externally to the articular surfaces, above and below. It is in relation internally with the circum- ference of the interarticular fibrocartilage, and lined by synovial membrane. The anterior, posterior, and lateral parts of the capsule are continuous in such a manner as to encapsulate the joint. (See Gray’s Anatomy.) The External Lateral ligament is the strongest part of the capsule. It is attached to the outer surface of the zygoma and to the outer surface of the neck of the condylar process. The synovial membrane lines the compartments of the capsule. cao N fi PROCESS Fig. 14, PTERYGOIDEUS EXTERNUS, ‘Temporomandibular articulation in sagittal section. (GxRaisH after TestvT.) The upper is larger and looser than the lower. The nerve-supply of this articu- lation is derived from the masseteric and auriculotemporal branches of the inferior maxillary division of the trifacial nerve. The muscles of mastication move the temporomandibular articulation ; they are supplied by the trifacial nerve ; hence the nerve-supply of the temporomandibular joint is from the trifacial and in har- mony with a general law. The interarticular fibrocartilage divides the cavity of the temporomandibular articulation into an upper and a lower portion. It has an upper part accommodated to the surface, over which it glides—concavo-convex antero-posteriorly ; a lower part, corresponding to the articular surface of the ‘Temporomandibular articulation, mesial view. (GenuisH after TesTuT.) condyle. The circumference of the cartilage, thicker than the central part, is attached to the inner surface of the delicate, loose, flabby, capsular ligament. A few fibres of the external pterygoid muscle are inserted into the anterior part of the cartilage, and by these the same is drawn forward onto the eminentia articu- laris when the mouth is opened. The Sphenomandibular (long internal lateral) ligament of the jaw extends from the spine of the sphenoid to the lingula of the mandible, Near the mandibular foramen thi ment is perforated by the mylohyoid nerve. Morphologically, 36 A MANUAL OF DISSECTION. it is a degenerated part of the first visceral arch. Its inner surface is in relation with the internal pterygoid muscle ; outer, with the external pterygoid muscle, middle meningeal artery, mandibular nerve, and internal maxillary vessels. The Stylomandibular ligament is between the masseter and internal pterygoid muscles, It arises from the styloid process near the apex, and is inserted into the posterior border and angle of the mandible. It is of fascial derivation. Embryology. The temporal bone consists of three genetically distinct parts— petrous, tympanic, and squamous—which at birth are separate from one another. The Tympanic is the smallest of the three embryonal parts of the bone, and is wedged in between the petrous and squamous parts at the base of the skull in such a way as to form (1) the auditory process around the external auditory canal ; (2) the vaginal process and tympanic plate, which latter forms a partition between the middle ear and the glenoid fossa. Union between the tympanic and squamous parts of the bone occurs before birth. Union also occurs between the tympanic and petrous parts, except in the region of the dorsal end of the first visceral arch, Failure to unite here is known as the Glaserian or petrotympanic fissure, located between the articular and non-articular parts of the glenoid fossa. In near rela- tion with the three parts of the temporal bone in the embryo were developing, from an entirely different source, mandible, tympanum, Eustachian tube, bones of hearing, and styloid process, We must see now how these opposite factions became so firmly amalgamated as to make a comprehensive understanding of the adult temporal bone, in its relation to the organs of hearing and mastication, without embryological study an absolute impossibility. We refer to the adjacency of the dorsal extremity of the visceral arches and clefts to the genetic parts of the temporal bone. The first and second visceral arches and their intervening cleft evolved the bones of hearing, the middle ear, the Eustachian tube, the stylomandibular and spheno- mandibular ligaments, the styloid process, and jaw bones before the development of the cranium : the petrosa was subsequently built up completely around the middle- ear parts, and incompletely about the condyle of the mandible, hence the tympanum and glenoid cavity ; perfect union between the tympanic part and petrosa did not occur, hence the Glaserian fissure wedging in the processus gracilis of the malleus. Table showing the parts in the temporomandibular region, evolved from (1) temporal bone ; (2) visceral arches. Temporal elements, Visceral arch structures, Auditory process. Condyle of mandible. Vaginal process. Styloid process, ‘Tympanic plate. Stylomandibular ligament, Posterior glenoid tubercle. Sphenomandibular ligament. Anterior glenoid tubercle and eminentia articularis, Tympanic cavity. Glenoid fossa. Eustachian tube. Glaserian fissure and canal of Huguier. Ossicles of hearing. DEPRESSIONS AND CANALS. The locations of depressions and canals in the temporomandibular region, according to the lines of least resistance and junctional areas, are the following : 1, The Glenoid Fossa is located between the tympanic and the squamous parts of the temporal bone. It lodges (a) condyle of the mandible ; (4) portion of the parotid gland. 2, The Glaserian Fissure is located between the tympanic and petrous portions of the temporal bone. It represents the ununited region between these two parts. It has a subdivision, the canal of Huguier or iter chord anterius, through which the chorda tympani passes from the midile ear to the z atic fossa. 3, The Auricular Fissure is between the auricular of the tympanic part and the mastoid process of the petrosa. The fissure transmits the auricular THE FACE. 37 branch of the vagus. This branch supplies the auricular process and communi- cates with the auriculotemporal branch of the trifacial nerve. 4, The Tympanum or middle ear, like the facial canal, is in a junctional area, determined by ossification proceeding from the four ossific nuclei of the petrosa. It was evaginated from the inner part of the first visceral cleft and completely surrounded by the petrosa. 5. The Facial Canal extends from the bottom of the internal auditory meatus to the stylomastoid foramen in the petrosa. It lodges the seventh nerve. Its jucctional area is determined by the ossification from the opisthotic, pterotic, pro-otic, and epiotic nuclei of the petrosa. DEPRESSOR AGENTS OF MANDIBLE. The depressors of the mandible are the following: 1. Gravity—that is, the weight of the jaw. 2. The platysma myvides muscle. 3. The digastric muscle. 4, The mylohyoid muscle. 5. The geniohyoid muscle. These agents are antago- nized by the following muscles : (a) The anterior segment of the temporal muscle. (6) The masseter muscle. (c) The internal pterygoid muscle. Nerve-supply. The nerve-supply is in harmony with the general rule: nerves that supply the muscles moving a joint supply the joint moved by the muscles. The fifth nerve supplies the muscles of mastication ; it also supplies the temporo- mandibular articulation through (1) the articular branch of the auriculotemporal ; (2) the articular branches of the masseteric. Blood-supply. The blood-supply is from the ascending pharyngeal branch of the externa! carotid, middle meningeal, and temporal branches of the internal maxillary artery. Ligamentous Muscles. The ligamentous muscles of the temporomandibular articulation are the temporal, masseter, internal, and external pterygoids. Muscles that cross any joint are said to be ligamentous thereto; they are the elastic ligaments, in contradistinction to the periosteal ligaments. INTERNAL MAXILLARY ARTERY. The internal maxillary artery arises from the external carotid in the substance of the parotid gland, behind the neck of the jaw. It traverses the zygomatic fossa, passes between the upper and lower heads of the external pterygoid muscle, and gives off its terminal branches in the sphenomaxillary fossa, “It has three portions: maxillary, pterygoid, and sphenomaxillary, and an accompanying internal maxillary vein. Braxcnes oF INTERNAL MAXILLARY, TABULATED. Maxillary portion, Plerygoi portion. Sphenomazillary portion. Deep auricular. Masseteric. Posterior dental (alveolar). Tympanic. Deep temporal. Infra-orbital. Middle meningeal. Plerygoid. The Vidian. Small meningeal. Buceal. ‘The pterygopalatine. Inferior dental, The sphenopalati ‘The ascending palatine. The descending palatine. The Maxillary Portion is between the neck of the jaw and the internal lateral ligament. From this are given off the following branches : (1) The deep auricu- lar, to the external auditory meatus and drum ; (2) the tympanic, which passes through the Glaserian fissure to the middle ear ; (3) the middle meningeal, given off between the neck of the jaw and the internal lateral ligament, passes between the two roots of the auriculotemporal nerve, through the foramen spinosum, in