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lower fibres alone of the orbicularis contract, and the lower lid is elevated. The elevation of the upper lid, as in opening the eye, is due to the levator palpebree superioris, which, arising within the orbit, is inserted into the upper eyelid. Muscles are inserted into the framework of the nostrils so as to increase or diminish the size of their orifices, and thus to promote or impede the passage of air into the nose. The size of the orifice is increased by two elevator muscles inserted into the ala, or side of the nostril; and when violent exercise is being performed, or respiration is from any cause impeded, the nostrils are always widely dilated. One of these elevator muscles, which also sends a slip down to the upper lip, and is consequently called the common elevator, is the muscle by the contraction of which a sneer is expressed. A partial closure of the nostril can be effected by small muscles which depress and compress the alze of the nose: in man these muscles are rudimentary as compared with the seal and other aquatic mammals, in which a powerful sphincter muscle closes the nostrils in the act of diving. The lips can be elevated or depressed so as to close or open the mouth; they can be protruded or retracted, or the corners of the mouth can be drawn to one side or the other, by the action of various muscles which are inserted into these movable folds of the integument. The orbicularis oris is a sphincter muscle, the fibres of which lie both in the upper and lower lips; by its contraction the mouth is closed and the lips pressed against the teeth, as when a firm resolution is intended to be expressed. The mouth is opened by the elevator muscles of the upper and the depressors of the lower lip ; it is transversely elongated by the zygomatic and risorius muscles, which pass to its corners, and which are brought into action in the acts of smiling and laughing. But the muscles of the lips also play an important part in connection with the reception of food into the mouth, and with the act of articula- _ tion. w ,. The cavity of r’ f I; . the mouth forms " ~‘ the commence- , ment of the ali- , mentary canal, 1‘ and is lined by a soft mucous membrane. In it the teeth and tongue are situated, and into it the secretion called saliva is poured. It opens behind into the pharynx. The side walls of the month are called the cheeks, and into the formation of each check a flattened quadrilateral muscle, the buccinator, enters. This muscle is attached above and below to the upper and lower jawbones, behind to constrictor muscle
Flo. 20.—Profile of cheek and pharynx. a, bucrtnator; b, tensor; c, levotur pslati; d, 1,], superior, middle, and inferior constrictors; g, thyro-hyoid; h, hyoglossus; l, mylo-hyoid; m, crlco-thyroid; n, stylephlryngeus; o, stylo-glossus; q, fibrous band whlch gives origin to bucclnstor and superior eonstrlcior; 1. gleam-pharyngeal nerve; 2. superior laryngeal artery; 3, superior laryngeal nerve; 4, its branch to crlcothyrold; 6, inferior laryngeal nerve and artery.
a fibrous band, to which the upper is also connected, so that the walls of
the mouth and pharynx are continuous with each other, whilst in front the buccinator blends with the structures in the lips. It compresses the cheeks, and drives the air out of the cavity of the mouth as in playing a wind instrument 3 hence the name, “ trumpeter’s muscle.”
The aperture of communication between the mouth and pharynx is named the isthmus of the fauces. It is bounded below by the root of the tongue, on each side by the tonsils, and above by the soft palate. The soft palate is a structure which hangs pendulous from the posterior edge of the hard bony palate. From its centre depends an elongated body, the mmla, and from each of its sides two folds extend, one downwards and forwards to the tongue, the other downwards and backwards to the pharynx. These folds are called the anterior and posterior pillars of the fauces or palate. Between the anterior and posterior pillar, on each side, the tonsil is seated. The soft palate and its pillars are invested by the mucous lining of the mouth and pharynx, and contain small but important muscles. The muscles of the soft palate and uvula, termed the elevators and tensors, raise and make them tense during the process of deglutition. The muscles of the posterior pillars, or palato-pharyngei, by their contraction, approximate the walls of the pharynx to the soft palate and uvula, whilst the muscles of the anterior pillars, or palato-glossi, diminish the size of the fauces.
goes from the mouth to the oesophagus in the act of swallowing, and through which the air is transmitted from the nose or mouth to the larynx in the act of breathing. It lies immediately behind the nose, mouth, and larynx, and in front of the five upper cervical vertebrae. Its length is from 4% to 5% inches ,its widest part is opposite the back of the mouth. Theprincipal muscles in its walls are called the constrictors, and are named, from above downwards, superior, middle, and in ferior. They are arranged in pairs, and arise from the cartilages of the larynx, from the hyoidbone,lower jaw, andinternal pterygoid process of the sphenoid; whilst the superior also springs from the fibrous band to which the buccinatoris attached ; their fasciculi curve backwards to the middle line of the posterior wall of the pharynx, to be inserted into a tendinous band which extends longitudinally along this wall of the tube.
The action of the muscles of the mouth, palate, and pharynx may now be considered in connection with the
Fro. 21.—Interior of the pharynx, seen by opening its posterior wall, a. a, Eustachian tube; b. b, tensor; 6, levator pulatl; d. levntor uvulm; e, a. pnlsto-phnryngeus; f, paIato-glossul; g. h. k. the three constrictors; I, I, tonsill.
’ rated and moistened, the palato-glossi relax, the tip of the
tongue is pressed against the roof of the mouth, and by a heave backward of that organ the bolus is pressed through the posterior orifice of the mouth into the pharynx, where it is grasped by the superior constrictor muscles, and forced downwards by them and the other constrictor muscles into the oesophagus, and thence into the stomach. As both the nose and larynx open into the pharynx, the one immediately above, the other immediately below the orifice of the mouth, it is of great importance that none of the food should enter into these chambers, and obstruct the respiratory passages. To guard against any accident of this kind, two valvular structures are provided,——viz., the soft palate and the epiglottis,—which, whilst leaving the orifices into their respective chambers open during breathing, may effectually close them when deglutition is being performed. As the bolus is being projected through the fences into the pharynx, the soft palate and uvula are elevated and made tense, and at the same time the wall of the pharynx is brought in contact with it by the contraction of the palatopharyngei ; the part of the pharynx intowhich the nose opens is thus temporarily shut off from that into which the mouth opens. If laughter, however, be excited at this time, the tension of the soft palate is destroyed, and part of the food may find its way upwards into the nose. The closure of the larynx by the epiglottis is due partly to the depression of that valve and partly to the elevation of the larynx. The backward heave of the tongue relaxes the ligaments which connect the front of the epiglottis to that organ, and enables the small epiglottidean muscles to depress the valve. The elevation of the hyoid and larynx is due to the action of the mylo-hyoid, digastric, and genio-hyoid muscles, which pass from the lower jaw to the hyoid, and of the thyro-hyoid, which pass from the hyoid to the thyroid cartilage of the larynx; preliminary to their action, the lower jaw must be fixed, which is done by the closure of the mouth prior to the act of swallowing. The aperture of the larynx is thus brought into contact with the depressed epiglottis, which is adapted more exactly to the opening by a change in its form due to the projection of a cushionlike pad from its posterior surface. By these ingenious arrangements the adaptation of a single chamber to the very different functions of breathing and swallowing is effectually provided for.
Jom'rs AND MUscLas or THE UPPER Lnun.
The upper limb is jointed to the trunk at the sterneclam'oular articulation. This is a diarthrodial joint: the bones are retained together by investing ligaments; a meniscus is interposed between the articular surfaces, so that the joint possesses two synovial membranes. A strong ligament, which checks too great upward movement, connects the clavicle and first rib. The two bones of the shoulder girdle articulate with each other at the diarthrodial (wromiodavicular joint ; but, in addition, a strong ligament, which checks too great displacement of the bones, passes between the clavicle and eoraeoid. The movements of the upper limb on the trunk take place at the sternoclavicular joint, and consist in the elevation, depression, and forward and backward movement of the shoulder. The movements at the acromio'clavicular joint occur when the scapula is
rotated on the clavicle 1n the act of elevating the arm above the head. The muscles which cause these movements are inserted into the bones of the shoulder girdle; the trapezius into the clavicle, acromion, and spine of the scapula; the rhomboid, levator anguli scapulzn, and serratus magnus into the vertebral border of the scapula; the pectoralis minor into the coracoid; and the subclavius into the clavicle. Elevation of the entire shoulder, as in shrugging the shoulders, is due to the contraction of the trapezius, levator scapulze, and rhomboideus ; depression partly to the weight of the limb and partly to the action of the subclavius and pectoralis minor; movement forward to the serratus and pectoralis; and backward to the trapezius and rhomboid. In rotation of the scapula on the clavicle, the inferior angle of the scapula is drawn forward by the serratus and lower fibres of trapezius, and backward by the levator scapulae, rhomboid, and lesser pectoral.
The Shoulder Joint is a ball-and-socket joint, thebal] _Sh0ull>r being the head of the humerus, the socket the glenoid fossa 1°11"
of the scapula. A large capsular ligament, which is pierced by the long tendon of the biceps muscle, and lined by a synovial membrane, encloses the articular ends of the two bones, and is so loose as to permit a range of movement greater than takes place in any other joint in the body. The muscles which cause these movements are inserted into the humerus; the supra-spinatus, infraspinatus, and teres minor into the great tuberosity; the sub-scapularis into the small tuberosity; the lstissimus dorsi and teres major into the bottom of the bicipital groove; the pectoralis major into its anterior border; the coraco-brachialis into the inner aspect, and the deltoid, which forms the fleshy prominence of the shoulder, into the outer aspect of the shaft. Abduction and elevation or extension of the arm outwards at the shoulder jointare due to the supra-spinatus and deltoid; adduction or depression, to the coraco-brachialis, latissimus, and terea major, assisted by the weight of the limb; movement forwards and elevation, to the anterior fibres of the deltoid, pectoralis, and subscapularis; backward movement to the latissimus and teres ; rotation outwards to the infra-spinatus and teres minor; rotation inwards to the subscapularis, pectoralis, latissimus, and teres. A combination of abduc tion, movement forwards, adduction, and movement backwards, produces the movement of circumduction. Certain movements of the upper limb, however, take place not only at the shoulder joint, but between the two bones of the shoulder girdle; for in elevating the arm, whilst the sup!“spinatus and deltoid initiate the movement at the shoulder joint, the farther elevation, as in raising the arm above the head, takes place by the trapezius and serratus, which rotate the scapula and draw its inferior angle forward. Th0 free range of movement of the human shoulder is one of its most striking characters, so that the arm can be moved in every direction through space, and its efiiciency as an instrument of prehension is thus greatly increased. The movement of abduction, or extension, which elevates the arm in line with the axis of the scapula, is characteristically human’ and a distinct Flo. '.'2.-Ontllne sketch of hnmll m1‘ articular area is provided on meme The mlmzll'tgmsfirof‘m the head of the humerus for xiii-tailors; 8mm.)
The Elbow Joint is the articulation between the human?’ radius, and ulna: the great sigmoid cavity of the "1m 1‘; adapted to the trochlea of the humerus, and the “up 0 the radius to the capitellum. The joint is enclosed by a
capsular ligament lined by a synovial membrane, which is subdivided into anterior, posterior, internal, and external bands of fibres. Flexion and extension are the two movements of the joint, and the range of movement is limited by the locking at the end of fiexion of the coronoid process into the coronoid fossa of the humerus, and at the end of extension of the olecranon process into the olecranoid fossa. The elbow joint is a hinge with screwed surfaces ; the path described by the hand and fore-arm is a spiral, so that during flexion they are thrown forwards and inwards. The muscles which cause the movements are inserted into the bones of the fore-arm. The fiexors are the brachialis anticus, inserted into the coronoid of the ulna; the biceps, which forms the fleshy mass on the front of the upper arm, into the tuberosity of the radius ; the supinator longus into the styloid process of the radius. The only extensor is the triceps-anconeus, which forms the fleshy mass on the back of the upper arm, and is inserted into the olecranon.
The Radio-ulnar Jaime are found between the two bones of the fore-arm. The head of the radius rolls in the lesser sigmoid cavity of the ulna, and is retained in position by a ring-like ligament which surrounds it 3 the shafts of the two bones are connected together by the interosseous membrane, their lower ends by a capsular ligament and a triangular fibre-cartilage or meniscus. The radius rotates round an axis drawn through the centre of its head and the styloid process of the ulna; rotation of the fore-arm and hand forward is called pronation,—rotation backwards, supination. The supinator and pronator muscles are all inserted into the radius : the supinators are the longus and brevis and the biceps; the pronators are the teres and quadratus. Where delicate manipulation is required the fore-arm is semi-flexed on the upper arm, for the cupshaped head of the radius is then brought into contact with the capitcllum of the humerus, and the rotatory movements of the bone can be performed with greater precision.
The Wrist or Radiacarpal Joint is formed above by the lower end of the radius and the triangular meniscus, below by the upper articular surfaces of the scaphoid, semi-lunar, and cuneiform bones. An investing ligament, lined by a synovial membrane, and subdivided into anterior, posterior, internal, and external bands of fibres, encloses the joint. It is the oblong form of hinge-joint, and possesses two axes, a long and a short; around the long axis movements occur which bend the hand forwards, or bring it in line with the fore-arm, or bend it backwards ; around the short axis the hand may be moved towards the radial or ulnar margins of the forearm. The fiexors forward are the palmaris longus, inserted into the palmar fascia ; the fiexor carpi radialis into the metacarpal bone of the index; the ficxor carpi ulnaris into the pisiform bone; the extensors and flexors backwards are the longer and shorter radial extensors inserted into the metacarpal bones of the index and middle fingers, and the ulnar extensor into the metacarpal bone of the little finger; the fiexors and extensors of the fingers have also a secondary action on the wrist joint. The ulnar flexor and ulnar extensor of the wrist draw the hand to the ulnar side, and the radial flexor and extensor, together with the extensors of the thumb, draw the hand towards the radial border of the fore-arm.
The Carpal and Came-metacarpal Joints are constructed thus :—The articular surfaces are retained in contact by certain ligaments passing between the dorsal surfaces of adjacent bones, by others between their palmar surfaces, and by interosseous ligaments between the semi-lunar and cuneiform, semi-lunar and scaphoid, os magnum and unciform, as magnum and trapezoid ; lateral ligaments also attach the scaphoid to the trapezium, and the cuneiform to the unciform. Similarly, the trapezoid, os magnum, and
unciform are connected to the metacarpal bones of the fingers by dorsal, palmar, and interosseous ligaments, and the metacarpal bones of the fingers have a like mode of union at their carpal ends 3 further, a transverse ligament extends between the distal ends of the metacarpal bones of the fingers, and checks too great lateral displacement. The range of movement at any one of these carpal joints is very slight, but the multiplicity of joints in this locality contributes to the mobility of the wrist, and makes the junction between the hand and fore-arm less rigid in its nature. The metacarpal bone of the thumb is not jointed to the index, and has a distinct saddle-shaped articulation with the trapezium, invested by a capsular ligament, so that its range of movement is extensive.
' The illelacarpo-phalangeal and Inter-plzalangeal Jointe Joints of are connected by lateral ligaments passing between the fingem
bones, and by an arrangement of fibres on their dorsal and palmar surfaces.
In studying the muscles which move the digits, it will be advisable, on account of the freedom and importance of the movements of the thumb, to examine its muscles independently. These muscles either pass from the fore-arm to the thumb, or are grouped together at the outer part of the palm, and form the elevation known as the ball of the thumb ; they are inserted either into the metacarpal bone or the phalanges. The thumb is extended and abducted, i.e., drawn away from the index, by three extensormuscles descending from the fore-arm, and inserted one into each of its three bones, and a small muscle, specially named abductor pollicis, inserted into the outer side of the first phalanx: its bones are bent on each other by a long and short flexor muscle ,I it is drawn back to the index by an adductor muscle; and the entire thumb is thrown across the surface of the palm by the opponens pollicis, which is inserted into the
Fm. 234—Deep muscles of the palm (I the hand. 1. abductor polllcls til-l short; 2, opponens; 8 und4, lubdivlslons of flexor brevll; ladductor; 8, 6’, tendon of long flexor pollicls; 1, abductor of the little ringer: 8, short flcxor; 9, opponens; 10, tendon of flcxor camiulnaril: 11. tendon of long supinntor; H transverse metacarpal ligament
shaft of the metacarpal bone.
The four fingers can be either bent, or extended, or drawn asunder, i.e., abducted; or drawn together, La, adducted.
The ungual phalanges can be bent by the
Fro. 24.—Tendons attached to a finger. a, the extensor tendon; 6, deep flerer. C,lllp0rfi¢lul flcxcr; d, s lnmbflcal muscle; e. an lnterosscnnl muscle; /, tcndlnous expansion from the lumbrlcal and lnterosscous muscles joining the extensor tendon.
action of the deep flexor muscle, the four tendons of which
are inserted into them ; the second phalanges by the super
ficial fiexor, also inserted by four tendons, one into each phalanx; these muscles descend from the front of the forearm into the palm in front of the wrist, where they are