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tremities, one of which is the head or the origin, the other but as contraction goes on they become more nearly perthe insertion. The belly is the fleshy part of the muscle, pendicular, so that they act with more advantage near and possesses a deep-red characteristic colour; it is the the close than at the commencement of contraction. If a active contractile structure, the source

muscle passes over only one joint, it acts on that joint only: of motor power. The two extremities

but if it passes over two or more joints, it acts on them in are called the tendons of the muscle,

succession, beginning with the joint next the point of or sinews; the tendons are bluish

insertion. A given movement may be performed by the white in colour, possess no power of

contraction of a single muscle, but as a rule two or more contractility, and are merely, as it

to muscles are associated together, and they are not unfrewere, the ropes by which the belly

quently so arranged that one muscle initiates the moveof the muscle is attached to the bone

ment, which is then kept up and completed by the rest. or other structure which is moved by

Muscles producing movement in one direction have opposed its contraction. The term tendon of

to them muscles which by their contraction effect the origin, applied to one extremity of the

opposite movement; when both groups act simultaneously muscle, signifies the fixed end of the

and with equal force, they antagonise each other, and no muscle, that to which it draws during

motion is produced; when a muscle is paralysed or divided, its contraction; as a rule this is the

its antagonistic muscle draws and permanently retains the end nearest the trunk, the proximal

LR part to its own side. The rapidity of action of a muscle is end. The term tendon of insertion is

proportioned to the length of its fasciculi, its power of applied to the end which is moved by

contraction to their number. the contraction; as a rule this is the

Each muscle is invested by a sheath formed of connective end most removed from the trunk,

tissue. In the limbs and in the neck not only has each the distal end. Entering the sub

muscle a sheath, but a strong fibrous membrane envelopes stance of each muscle is at least

the whole of the muscles, and assists materially in giving one artery, which conveys blood for its

form and compactness to the region. This membrane is called nutrition; this artery ends in a net

generally a fascia or aponeurosis, but special descriptive work of capillary blood vessels, from

names are given to it in the different regionse.g., cervical which a vein arises and conveys the

fascia, brachial aponeurosis, fascia lata, or fascia of the blood out of the muscle again; an

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thigh. In some localities muscles arise from the fascia, other small vessel, called a lymphatic,

and in others they are inserted into it. The fascia is

L.ti also arises within the muscle, and

separated from the skin by a layer of subcutaneous fatty conveys the fluid lymph out of the

tissue, and in this layer muscles are in some localities demuscle. Each muscle also is pene

veloped. In the fat of the inner border of the palm of the trated by a nerve, through which it

hand a small muscle, the palmaris brevis, is found, which is brought into connection with the

is inserted into the skin covering the ball of the little brain, so as to be subject to the in- Fig. 18.—The rectus muscle finger; at each side of the neck, also, lies a thin muscle fluence of the will. The will is the of the thigh; to show called platysma myoides, and the muscles on the face and

the constituent parts of a natural stimulus for exciting muscular , the fleshy scalp which move the skin of the face and head belong to action, which action is in many cases

the same category. These muscles form the group of sub80 rapid that scarcely an appreci tion; 71, nerve of supply; cutaneous or dermal muscles which, except in the localities able interval of time intervenes be

a, artery of supply; o,
vein; l, lymphatic vessel;

above referred to, are not represented in the human body, tween willing and doing the action.

P, the patella.

but are well known in the bodies of the mammalia geneThe bones form a series of rod-like levers, and, in study- rally as the panniculus carnosus. ing the mode of action of the muscles, the place of inser In arranging the muscles for descriptive purposes, either tion of the muscle into the bone—that is to say, the point a morphological, a topographical, or a physiological method of application of the power which causes the movement may be pursued. The morphological arrangement is to be and its relations to the joint, or fulcrum, or centre of motion, preferred when the object is to compare the muscular and to the weight or resistance which is to be overcome, system in man with that in different animals, and the basis have to be kept in view. The relative positions of ful of the arrangement should be into muscles of the axial, crum, point of application of power, and resistance, are not the appendicular, and the axi-appendicular skeletons, and the same in all the bony levers. As a rule, the muscles sub-cutaneous muscles; a topographical arrangement is most are inserted into bones between the fulcrum and the move suitable for the purposes of the practical surgeon; a physioable point of resistance, and nearer the fulcrum than the logical arrangement, when the object is to study the action movable point, as may be seen in the muscles which bend of the muscles in connection with the movements of the the fore-arm at the elbow-joint. Although from the weight- joints. In Plates XV. and XVI., a front and back view arm of the lever being in these cases much longer than the of the voluntary muscles of the body is given. power-arm, the muscles, as regards the application of the

JOINTS AND MUSCLES OF THE AXIAL SKELETON. power, act at a disadvantage, yet the movement gains in velocity. Sometimes the muscle is inserted, as is the The Intervertebral Joints are complex in construction. Intervention case in the great muscle which straightens or extends The bodies of the true vertebræ are connected together by bral jours the fore-arm, at one end of the lever, and the fulcrum an amphiarthrodial joint: the fibro-cartilaginous plate or or joint is placed between it and the movable point. At intervertebral disc is tough and fibrous in its peripheral other times, as in the case of the chief depressor muscle part, but soft and pulpy within. (Fig. 15.) Remains of the of the lower jaw, whilst the muscle is attached to one end chorda dorsalis are said to occur in the soft pulp, and someof the lever, the fulcrum is at the opposite end. When a times a distinct cavity, lined by a synovial membrane, is muscle is so placed that its tendon of insertion is perpen- found in the centre of the disc, which in the finner whales dicular to the bone to which it is attached, it acts to great is expanded into a large central cavity containing many advantage; when placed obliquely or nearly parallel, a loss ounces of synovia. A diarthrodial joint connects the supoof power occurs. Many muscles at the commencement of rior and inferior articular processes of adjacent vertebræ on contraction lie obliquely to the tones which they move, each side. Elastic yellow ligaments, the ligamenta subflava,

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pass between their laminæ. Inter- and supra-spinous liga- | bones and joints play but a small part. The lumbar Muscles of ments connect adjacent spinous processes, and in the neck vertebræ behind, the expanded wings of the iliac bones abdomen. the supra-spinous ligament forms a broad band, the liga- below, and the false ribs above, are the only bones to be mentum nucho. In those mammals which possess big considered. Three pairs of greatly expanded muscles heads or heavy horns, this ligament of the back of the the external oblique, internal oblique, and transverse-lie neck forms a powerful elastic band for the support of the at the sides and in front, and two pairs of muscles the head. The joints between the atlas and axis, and the recti and pyramidales—are situated wholly in front. The atlas and occiput, are specially modified in connection with internal oblique and the transverse muscles are attached the movements of the head on the top of the spine. The above to the ribs, behind to the lumbar spine, below to the intervertebral discs are absent, and the range of movement iliac crest and to a strong band, Poupart's ligament, extendeither from before backward, as in nodding the head, or ing from the crest of the ilium to the pubic spine; the exfrom side to side, as in looking over the shoulder, are ternal oblique has similar connections above and below, but more extensive than between any of the other true vertebræ. is not attached behind to the lumbar spine. The muscles The head rotates along with the atlas around the odontoid all terminate in front in strong expanded tendons, called or pivot process of the axis, which is lodged between the the anterior abdominal aponeuroses, which blend together in anterior part of the atlas and a strong transverse ligament the middle line anteriorly to form the band called linea which lies behind the odontoid. Too great movement to alba, which stretches longitudinally from the xiphi- ternum one side or the other is prevented by the check ligaments, to the pubic symphysis.

to the pubic symphysis. These expanded tendons enclose which

pass from the top of the odontoid to the occipital the recti muscles, which pass from the pubis upwards to bone, in front of the foramen magnum. The nodding the cartilages of the lower true ribs, and the pyramidal movements take place between the occiput and atlas, and muscles, which pass from the pubis to be inserted into the are permitted by the size and shape of the occipital condyles linea alba. The entire arrangement is admirably adapted and hollow upper articular surfaces of the atlas. These for completing the walls of the great abdominal chamber, joints are all diarthrodial. The spine is flexible and and for enabling the muscles to compress the abdominal elastic; except in the joints above referred to, the range viscera, an action which takes place when the contents of of movement between any two true vertebræ is very small, the bowels and bladder are being expelled during defæcabut the sum of the movement in the entire spine, owing to tion and micturition. the number of bones, is considerable. The elasticity of Bones and joints play a more important part in the the spine is partly due to the numerous diarthrodial joints formation of the walls of the thoracic than of the abdobetween its articular processes, but more especially to the minal cavity. Not only are there thoracic vertebræ behind, discs of fibro-cartilage interposed between the bodies of and the sternum in front, but on each side the twelve ribs the vertebræ, which act like elastic pads or buffers to pre- arch more or less completely forward from the spine ; each vent shock. The spine and trunk may be bent either rib is articulated behind to one or two vertebræ, and the forwards or backwards, or to the right and left side ; or seven upper ribs, through their costal cartilages, articulate without being bent, the spine may be screwed to the right with the sternum. or to the left, the screwing movement being permitted by The Costo-vertebral Joints are situated between the head Costal the oblique direction of the articular processes.

of the rib and the vertebral body; also, except in the float-joints. The muscles which move the vertebræ on each other are ing ribs, between the tubercle of the rib and the transverse principally situated on the back of the trunk. In the process of the vertebra, the joints being diarthrodial, and hollow on each side of the vertebral spines lies the great completed in the usual manner by ligaments and synovial erector spinæ muscle, the fibres of which pass longitudin- membrane. The Costo-sternal Joints are also diarthrodial ally upwards. When both muscles act together, the entire (except the first costal cartilage, which is directly united to spine is bent back; but when the muscle of one side only the præ-sternum), a capsular ligament, lined by a synovial contracts, then the spine is bent to that side. These membrane, connecting the cartilages of the true ribs to the muscles also act in raising the spine from the bent to the sternum. The cartilages from the sixth to the ninth ribs erect position, and they are assisted by small inter-spinal are also united by ligamentous fibres. muscles, situated between the spines in the cervical and The movements of the ribs and sternum at the costo lumbar regions.

The spine is bent forward by the psoæ vertebral and costo-sternal joints are of the utmost importand longi colli muscles; and the straight muscles of the ance in the process of breathing. Breathing or respiration abdomen, inserted into the lower true ribs, assist in this consists of two acts—breathing in, or inspiration, and breathmovement. The screwing movements of the spine are ing out, or expiration. During inspiration, the air rushes effected by a series of muscles, the fibres of which pass through the nose or mouth down the windpipe, and dilates obliquely between the laminæ and spines of adjacent verte the air-cells of the lungs; together with the expansion of bræ, and are known as the semispinales, multifidi, and the lungs the walls of the chest rise, so that the capacity rotatores spinæ muscles.

both of lungs and chest at the end of a full inspiration is The head is balanced on the summit of the spine, and nearly doubled. During inspiration the following changes is maintained in a quiescent position without any appre occur in the walls of the chest : the ribs are elevated and ciable muscular action, but it can be moved in various rotated, the lower borders of their shafts are everted, directions by the muscles inserted into its bones. The while their surfaces are at the same time rendered more nodding movements of the head on the atlas are due to oblique, and the width of the intercostal spaces is thereby the posterior recti, the two superior obliques, the two increased; the elevation and rotation of the ribs throw splenii, and the two complexus muscles, which draw it the sternum upwards and forwards, and make the thoracic backwards, and the anterior recti and sterno-cleido-mastoid part of the spinal column straighter; the diaphragm is muscles, which draw it forwards. When the right splenius depressed, and the antero-lateral walls of the abdomen are and greater posterior rectus and inferior oblique act along thrown forward. The muscles which cause these movewith the left complexus and sterno-mastoid, the head is ments are as follows :-In each of the spaces between rotated to the right shoulder; the opposite rotation being the different ribs a pair of intercostal muscles is situated; due to the action of the corresponding muscles on the these elevate and rotate the ribs, and the movements are other side of the body.

assisted by the levatores costarum, and, in the case of the In the formation of the walls of the abdomen proper, , upper and lower ribs, by the scaleni and serrati pestici

muscles; and by these agents the transverse and antero- | hyoids, into their inner surfaces. The elevators of the jaw posterior diameter of the chest is increased. The increase are much more powerful than the depressors, for they not in its vertical diameter is due to the action of the dia- only have to overcome the weight of the bone, but during phragm or midriff, the great muscle which, arising by its mastication have to exercise force sufficient to cut or break circumference from the xiphi-sternum, six lower ribs, and down the food between the teeth. In carnivorous animals, bodies of the lumbar vertebræ, forms the floor of the thoracic more especially those which, like the tiger or hyæna, crack and the roof of the abdominal cavity. It constitutes a the bones of their prey, these muscles attain a great size. great arch, with its convexity directed to the cavity of the The lower jaw can be projected in front of the upper by the chest. By the contraction of its fibres the arch is rendered external pterygoid muscles, inserted into the neck of the less convex, and the floor of the chest is thereby depressed. bone on each side; but excessive movement forward is Under circumstances which require more powerful efforts checked by the action of the stylo-maxillary ligaments, of inspiration, the muscles which pass from the walls of which pass from the styloid processes to the angles of the the chest to the upper limbs may, by taking their fixed bone; when projected forward, the jaw is drawn back by points at the limbs, act as elevators of the ribs. During the posterior fibres of the temporal muscles. When the expiration the ribs are depressed, their lower borders in- elevator, depressor, protractor, and retractor muscles are verted, the width of the intercostal spaces diminished, the successively brought into action, the lateral or grinding stornum depressed, the spine more curved, and the dia- movements of the bone, so important in mastication, are

produced.

Along with the movements of the lower jaw those of the hyoid bone and larynx must be considered, for the digastrics, the genio- and mylo-hyoids, which depress the lower jaw, act, when their action is reversed, along with the stylohyoid muscles in elevating the hyoid bone and larynx, which structures can be depressed or drawn downwards by the action of the sterno-hyoids, sterno-thyroids, thyro

hyoids, and omo-hyoids; the elevation of the hyoid, when प

drawn down by its depressor muscles, is effected by the elastic stylo-hyoid ligaments attached to its small cornua, which, by their recoil when the depressor muscles have ceased to contract, draw the bone up to its former position.

Numerous muscles are situated immediately beneath the skin of the scalp and face. They are not of so deep red a colour as the muscles of the trunk and limbs, and whilst they arise from one or other of the bones of the head, they áre inserted into the deep surface of the skin itself. Hence when they contract they move the skin of the scalp and face, and as they are the instruinents through which the various passions and emotions are expressed, they are grouped to

gether as the Muscles of Expression (Plate XV., figs. 2 and Fig. 19.– The concave abdominal surface of the diaphragm. a, 4th lumbar 3). The occipito-frontalis, or great muscle of the scalp,

vertebra; b, c, 12th and 11th ribs; d, xiphi-sternum; e, f, crura of diaphragm ;
gh arched tendons of origin of diaphragm; k, aorta; ly csophagus; m,

passes from the occipital bone over the vertex to the foreinferior vena cava; n, psoas; 0, quadratus muscle; 999, central tendon of head; when it contracts, the skin of the forehead is wrinkled diaplıragm, into which the muscular fibres are inserted.

transversely, the eyebrows are elevated, and an expression phragm more convex. These movements are principally of amazement or surprise is produced. Some persons have a due to the recoil of the elastic tissue of the lungs previously greater power over this muscle than others, and by the alterrendered tense by the inflation of the air-cells, and to the nate contraction of its occipital and frontal portions can untwisting of the ribs when the inspiratory muscles cease move the hairy scalp to and fro with great rapidity. A pair to elevate and rotate them. Muscular action plays but a of muscles, the corrugatores supercilii, arises from the

suprasmall part in quiet expiration, but the expulsion of the ciliary ridges, on the frontal bone, to be inserted into the air from the lungs may be facilitated by contracting the eyebrows : they draw the eyebrows downwards and inabdominal muscles, which, pressing the abdominal viscera wards, wrinkle the skin of the forehead longitudinally, against the under surface of the diaphragm, force that and contract with great vigour in the act of frowning. muscle upwards.

The auricle of the external ear has three small muscles Joints and The Temporo-maxillary Joints are the only diarthrodial inserted into it, one behind, the posterior, one above, the nzuscles of articulations in the head. The condyle of the lower jaw on superior, one in front, the anterior auricular muscle : in the head. each side is received into the glenoid fossa of the temporal man, as a rule, these muscles are feeble, and have little

bone; each joint is enclosed by a capsular ligament, and action ; but in many mammals they are large, and by them between the articular surfaces is a meniscus, which sub- the animal pricks its ears to detect the faintest sound of divides the interior of the joint into two cavities, each lined danger. The eyelids are drawn together, so as to close the by a synovial membrane. The movements of the lower eye as in the act of sleep, by the orbicularis palpebrarum, jaw take place simultaneously at both its articulations the fibres of which lie in the eyelids and on the borders of during mastication and speech, through the action of the the orbit, and surround the fissure between the eyelids. several muscles which are inserted into it. This bone is This muscle is a characteristic specimen of the group of elevated by the temporal muscles, inserted into the coronoid sphincter muscles, i.e., muscles which surround orifices, and processes; and by the masseterics, inserted into the outer by their contraction close them. When the upper fibres of surface, and the internal pterygoids, into the inner surface of the muscle alone contract, the uoper eyelid is depressed, each angle. It is depressed partly by its own weight and a movement which takes place almost involuntarily and partly by the action of the digastrics and genio-hyoids, in with great frequency during our waking hours, so as to serted close to the symphysis; by the platysma, inserted into wash the tears over the exposed part of the eyeball and the outer surface of each horizontal ramus; and the mylo- | keep it moist. In expressing a knowing wink,” the

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