noted from it that there is no direct relation between the extent of a cortical area and the mass of muscles which it controls. The mass of muscles in the trunk is greater than in the leg, and in the leg is greater than in the arm, and in the arm is many times greater than in the face and head; yet for the last the cortical area is the most extensive of all, and for the first-named is the least extensive of all. The motor field of the cortex is, taken altogether, relatively to the size of the lower parts of the brain, larger in the anthropoid than in the inferior monkey brains. But in the anthropoid | Anus & vegira. Sulcus centralis Toes Knee... Shoulder Elbow Wrist Fingers &thumb... Eari LEG ARM Abdomen come to be furnished more and more with fibres that are fully myelinate. At the beginning of its history each is unprovided with myelinate nerve fibres. The excitable foci of the cerebral cortex are well myelinated long before the unexcitable are so. The regions of the cortex, whose conduction paths are early completed, may be arranged in groups by their connexions with sense-organs: eye-region, ear-region, skin and somaesthetic region, olfactory and taste region. The areas of intervening cortex, arriving at structural completion later than the above sense-spheres, are called by some association-spheres, to indicate the view that they contain the neural mechanisms of reactions (some have said "ideas") associated with the sense perceptions elaborated in the several sensespheres. Chest Sulcus centralis. Vocal Sensorimotor Centres. The name motor area" is given to that region of cortex whence, as D. Ferrier's investigations showed, motor reactions of the facial and limb muscles are regularly and easily evoked. This region is often called the sensori-motor cortex, and the term somaesthetic has also been used and seems appropriate. It has been found that disturbance of sensation, as well as disturbance of movement, is often incurred by its injury, Patients in whom, for purposes of diagnosis, it has been electrically excited, describe, as the initial effect of the stimulation, tingling and obscure but locally-limited sensations, referred to the part whose muscles a moment later are thrown into co-ordinate activity. The distinction, therefore, between the movement of the eyeballs, elicited from the occipital (visual) cortex, and that of the hand, elicited from the cortex in the region of the central sulcus (somaesthetic), is not a difference between motor and sensory, for both are sensori-motor in the nature of their reactions; the difference is only a difference between the kind of sense and sense-organ in the two cases, the muscular apparatus in each case being an appanage of the sensual. Nose of jaw. Closure Opening of jaw. Diagram of the Topography of the Main Groups of Foci in the Motor Field of Chimpanzeec. brain still more increased even than the motor field are the great regions of the cortex outside that field, which yield no definite movements under electric excitation, and are for that reason known as " silent." The motor field, therefore, though absolutely larger, forms a smaller fraction of the whole cortex of the brain than in the lower forms. The statement that in the anthropoid (orang-outan) brain the groups of foci in the motor fields of the cortex are themselves separated one from another by surrounding inexcitable cortex, has been made and was one of great interest, but has not been confirmed by subsequent observation. That in man the excitable foci of the motor field are islanded in excitable surface similarly and even more extensively, was a natural inference, but it had its chief basis in the observations on the orang, now known to be erroneous. In the diagram there is indicated the situation of the cortical centres for movement of the vocal cords. Their situation is at the lower end of the motor field. That they should lie there is interesting, because that place is close to one known in man to be associated with management of the movements concerned in speech. When that area in man is injured, the ability to utter words is impaired. Not that there is paralysis of the muscles of speech, since these muscles can be used perfectly for all acts other than speech. The area in man is known as the motor centre for speech; in most persons it exists only in the left half of the brain and not in the right. In a similar way damage of a certain small portion of the temporal lobe of the brain produces loss of intelligent apprehension of words spoken, although there is no deafness and although words seen are perfectly apprehended. Another region, "the angular region," is similarly related to intelligent apprehension of words seen, though not of words heard. When this differentiation of cortex, with its highest expression in man, is collated with the development of the cortex as studied in the successive phases of its growth and ripening in the human infant, a suggestive analogy is obvious. The nervous paths in the brain and cord, as they attain completion, That the lower types of vertebrate, such as fish, e.g. carp, possess practically no cortex cerebri, and nevertheless execute "volitional" acts involving high co-ordination and suggesting the possession by them of associative memory, shows that for the existence of these phenomena the cortex cerebri is in them not essential. In the dog it has been proved that after removal from the animal of every vestige of its cortex cerebri, it still executes habitual acts of great motor complexity requiring extraordinarily delicate adjustment of muscular contraction. It can walk, run and feed; such an animal, on wounding its foot, will run on three legs, as will a normal dog under similar mischance. But signs of associative memory are almost, if not entirely, wanting. Throughout three years such a dog failed to learn that the attendant's lifting it from the cage at a certain hour was the preliminary circumstance of the feedinghour; yet it did exhibit hunger, and would refuse further food when a sufficiency had been taken. In man, actually gross sensory defects follow even limited lesions of the cortex. Thus the rabbit and the dog are not absolutely blinded by remova! of the entire cortex, but in man destruction of the occipital cortex produces total blindness, even to the extent that the pupil of the eye does not respond when light. is flashed into the eye. Examination of the cerebellum by the method of Wallerian degeneration has shown that a large number of spinal and bulbar nerve cells send branches up into it. These Cerebellum. seem to end, for the most part, in the grey cortex of the median lobe, some, though not the majority, of them decussating across the median line. The organ seems also to receive many fibres from the parietal region of the cerebral hemisphere. From the organ there emerge fibres which cross to the opposite red nucleus, and directly or indirectly reach the thalamic region of the crossed hemisphere. The pons or middle peduncle, which was regarded, on the uncertain ground of naked-eye dissection of human | essentially nervous. In deep sleep the threshold-value of the anatomy, as commissural between the two lateral lobes of the cerebellum, is now known to constitute chiefly a cerebrocerebellar decussating path. Certain cerebellar cells send processes down to the cell-group. in the bulb known as the nucleus of Deiters, which latter projects fibres down the spinal cord. Whether there is any other or direct emergent path from the cerebellum into the spinal cord is a matter on which opinion is divided. Injuries of the cerebellum, if large, derange the power of executing movements, without producing any detectable derangement of sensation. The derangement gradually disappears, unless the damage to the organ be very wide. A reeling gait, oscillations of the body which impart a zigzag direction to the walk, difficulty in standing, owing to unsteadiness of limb, are common in cerebellar disease. On the other hand, congenital defect amounting to absence of one cerebellar hemisphere has been found to occasion practically no symptoms whatsoever. Not a hundredth part of the cerebellum has remained, and yet there has existed ability to stand, to walk, to handle and lift objects in a fairly normal way, without any trace of impairment of cutaneous or muscular sensitivity. The damage to the cerebellum must, it would seem, occur abruptly or quickly in order to occasion marked derangement of function, and then the derangement falls on the execution of movements. One aspect of this derangement, named by Luciani astasia, is a tremor heightened by or only appearing when the muscles enter upon action-" intention tremor." Vertigo is a frequent result of cerebellar injury: animals indicate it by their actions; patients describe it. To interpret this vertigo, appeal must be made to disturbances, other than cerebellar, which likewise occasion vertigo. These include, besides ocular squint, many spatial positions and movements unwonted to the body: the looking from a height, the gliding over ice, sea-travel, to some persons even travelling by train, or the covering of one eye. Common to all these conditions is the synchronous rise of perceptions of spatial relations between the self and the environment which have not, or have rarely, before arisen in synchronous combination. The tactual organs of the soles, and he muscular sense organs of limbs and trunk, are originating perceptions that indicate that the self is standing on the solid earth, yet the eyes are at the same time originating perceptions that indicate that the solid earth is far away below the standing self. The combination is hard to harmonize at first; it is at least not given as innately harmonized. Perceptions regarding the " me are notoriously highly charged with "feeling," and the conflict occasions the feeling insufficiently described as "giddiness." The cerebellum receives paths from most, if not from all, of the afferent roots. With certain of these it stands associated most closely, namely, with the vestibular, representing the sense organs which furnish data for appreciation of positions and movements of the head, and with the channels, conveying centripetal impressions from the apparatus of skeletal movement. Disorder of the cerebellum sets at variance, brings discord into, the space-perceptions contributory to the moyement. The body's movement becomes thus imperfectly adjusted to the spatial requirements of the act it would perform. In the physiological basis of sense exist many impressions which, apart from and devoid of psychical accompaniment, reflexly influence motor (muscular) innervation. It is with this sort of habitually apsychical reaction that the cerebellum is, it would seem, employed. That it is apparently devoid of psychical concomitant need not imply that the impressions concerned in it are crude and inelaborate. The seeming want of reaction of so much of the cerebellar structure under artificial stimulation, and the complex relay system revealed in the histology of the cerebellum, suggest that the impressions are elaborate. Its reaction preponderantly helps to secure coordinate innervation of the skeletal musculature, both for maintenance of attitude and for execution of movements. Sleep. The more obvious of the characters of sleep (q.v.) are stimuli for the various senses is very greatly raised, rising rapidly during the first hour-and a half of sleep, and then declining with gradually decreasing decrements. The muscles become less tense than in their waking state: their tonus is diminished, the upper eyelid falls, and the knee-jerk is in abeyance. The respiratory rhythm is less frequent and the breathing less deep; the heart-beat is less frequent; the secretions are less copious; the pupil is narrow; in the brain there exists arterial anaemia with venous congestion, so that the blood-flow there is less than in the waking state. Theories of It has been suggested that the gradual cumulative result of the activity of the nerve cells during the waking day is to load the brain tissue with "fatigue-substances" which clog the action of the cells, and thus periodi- Sleep cally produce, that loss of consciousness, &c., which is sleep. Such a drugging of tissue by its own excreta is known in muscular fatigue, but the fact that the depth of sleep progressively increases for an hour and more after its onset prevents complete explanation of sleep on similar lines. It has been urged that the neurons retract during sleep, and that thus at the synapses the gap between nerve cell and nerve cell becomes wider, or that the supporting cells expand between the nerve cells and tend to isolate the latter one from the other. Certain it is that in the course of the waking day a great number of stimuli play on the sense organs, and through these produce disintegration of the living molecules of the central nervous system. Hence during the day the assimilatory processes of these cells are overbalanced by their wear and tear, and the end-result is that the cell attains an atomic condition less favourable to further disintegration than to reintegration. That phase of cell life which we are accustomed to call "active" is accompanied always by disintegration. When in the cell the assimilative processes exceed dissimilative, the external manifestations of energy are liable to cease or diminish. Sleep is not exhaustion of the neuron in the sense that prolonged activity has reduced its excitability to zero. The nerve cell just prior to sleep is still well capable of response to stimuli, although perhaps the threshold-value of the stimulus has become rather high, whereas after entrance upon sleep and continuance of sleep for several hours, and more, when all spur to the dissimilation process has been long withheld, the threshold-value of the sensory stimulus becomes enormously higher than before. The exciting cause of sleep is therefore no complete exhaustion of the available material of the cells, nor is it entirely any paralysing of them by their excreta. It is more probably abeyance of external function during a periodic internal assimilatory phase. is close interconnexion between the two aspects of the double Two processes conjoin to initiate the assimilatory phase. There activity that in physiological theory constitute the chemical life of protoplasm, between dissimilation and assimilation. Hering has long insisted on a self-regulative adjustment of the cell metabolism, so that action involves reaction, increased catabolism necessitates after-increase of anabolism. The long-continued incitement to catabolism of the waking day thus of itself predisposes the nerve cells towards rebound into the opposite phase; the increased catabolism due to the day's stimuli induces increase of anabolism, and though recuperation goes on to a large extent during the day itself, the recuperative process is slower than, and lags behind, the disintegrative. Hence there occurs a cumulative effect, progressively increasing from the opening till the closing hours. The second factor inducing the assimilative change is the withdrawal of the nervous system from sensual stimulation. The eyes are closed, the maintenance of posture by active contraction is replaced by the recumbent pose which can be maintained by static action and the mere mechanical consistence of the body, the ears are screened from noise in the quiet chamber, the skin from localized pressure by a soft, yielding couch. The effect of thus reducing the excitant action of the environment is to give consciousness over more to mere revivals by memory, and gradually consciousness lapses. A remarkable case is well authenticated, where, owing to disease. a young man had lost the use of all the senses save of one eye and of one ear. If these last channels were sealed, in two or three minutes' time he invariably fell asleep. If natural sleep is the expression of a phase of decreased excit ability due to the setting in of a tide of anabolism in the cells of the nervous system, what is the action of narcotics? They lower the 24 away. external activities of the cells, but do they not at the same time | lower the internal, reparative, assimilative activity of the cell that in natural sleep goes vigorously forward preparing the system for the next day's drain on energy? In most cases they seem to lower both the internal and the external activity of the Narcotics. nerve cells, to lessen the cell's entire metabolism, to reduce the speed of its whole chemical movement and life. Hence it is not surprising that often the refreshment, the recuperation, obtained from and felt after sleep induced by a drug amounts to nothing, or to worse than nothing. But very often refreshment is undoubtedly obtained from such narcotic sleep. It may be supposed that in the latter case the effect of the drug has been to ensure occurrence of that second predisposing factor mentioned above, of that withdrawal of sense impulses from the nerve centres that serves to usher in the state of sleep. In certain conditions it may be well worth while by means of narcotic drugs to close the portals of the senses for the sake of thus obtaining stillness in the chambers of the mind; their enforced quietude may induce a period in which natural rest and repair continue long after the initial unnatural arrest of vitality due to the drug itself has passed Hypnotism.-The physiology of this 66 of group states" is, as regards the real understanding of their production, eminently vague (see also HYPNOTISM). The conditions which tend to induce them contain generally, as one element, constrained visual attention prolonged beyond ordinary duration. Symptoms attendant on the hypnotic state are closure of the eyelids by the hypnotizer without subsequent attempt to open them by the hypnotized subject; the pupils, instead of being constricted, as for near vision, dilate, and there sets in a condition superficially resembling sleep. But in natural sleep the action of all parts of the nervous system is subdued, whereas in the hypnotic the reactions of the lower, and some even of the higher, parts are exalted. Moreover, the reactions seem to follow the sense impressions with such fatality, that, as an inference, absence of will-power to control them or suppress them is suggested. This reflex activity with "paralysis of will" is characteristic of the somnambulistic state. The threshold-value of the stimuli adequate for the various senses may be extraordinarily lowered. Print of microscopic size may be read; a watch ticking in another room can be heard. Judgment of weight and texture of surface is exalted; thus a card can in a dark room be felt and then re-selected from the re-shuffled pack. Akin to this condition is that in which the power of maintaining muscular effort is increased; the individual may lie stiff with merely head and feet supported on two chairs; the limbs can be held outstretched for hours at a time. This is the cataleptic state, the phase of hypnotism which the phenomena of so-called "animal hypnotism resemble most. A frog or fowl or guinea-pig held in some unnatural pose, and retained so forcibly for a time, becomes "set" in that pose, or rather in a posture of partial recovery of the normal posture. In this state it remains motionless for various periods. This condition is more than usually readily induced when the cerebral hemispheres have been removed. The decerebrate monkey exhibits "cataleptoid" reflexes. Father A. Kircher's experimentum mirabile with the fowl and the chalk line succeeds best with the deccrebrate hen. The attitude may be described as due to prolonged, not very intense, discharge from reflex centres that regulate posture and are probably intimately connected with the cerebellum. A sudden intense sense stimulus usually suffices to end this tonic discharge. It completes the movement that has already set in but had been checked, as it were, half-way, though tonically maintained. Coincidently with the persistence of the tonic contraction, the higher and volitional centres seem to lie under a spell of inhibition; their action, which would complete or cut short the posture-spasm, rests in abeyance. Suspension of cerebral influence exists even more markedly, of course, when the cerebral hemispheres have been ablated. But a potent according to some, the most potent-factor in hypnotism, namely, suggestion, is unrepresented in the production of so-called animal hypnotism. We know that one idea suggests another, and that volitional movements are the outcome of ideation. If we assume that there is a material process at the basis of ideation, we may take the analogy of the concomitance between a spinal reflex movement and a skin sensation. The physical "touch" that initiates the psychical "touch" initiates, through the very same nerve channels, a reflex movement responsive to the physical "touch," just as the psychical "touch" may be considered also a response to the same physical event. good arguments for belief that we get the reflex movement alone But in the decapitated animal we have as response; the psychical touch drops out. Could we assume that there is in the adult man reflex machinery which is of higher order than the merely spinal, which employs much more complex motor mechanisms than they, and is connected with a much wider range of sense organs, and could we assume that this reflex machinery, although usually associated in its action with memorial and volitional processes, may in certain circumstances be sundered from these latter and unattendant on them-may in fact continue in work when the higher processes are at a standstill-then we might imagine a condition resembling that of the somnambulistic and cataleptic states of hypnotism. Such assumptions are not wholly unjustified. Actions of great complexity and delicacy of adjustment are daily executed by each of us without what is ordinarily understood as volition, and without one's watch from the pocket and look at it when from a familiar more than a mere shred of memory attached thereto. To take clock-tower a familiar bell strikes a familiar hour, is an instance of a habitual action initiated by a sense perception outside attentive consciousness. We may suddenly remember dimly afterwards that we have done so, and we quite fail to recall the difference between the watch time and the clock time. In many instances hypnotism seems to establish quickly reactions similar to such as usually result only from long and closely attentive practice. The sleeping mother rests undisturbed by the various noises of the house and engineer, engaged in conversation with some visitor to the engine street, but wakes at a slight murmur from her child. The ship's room, talks apparently undisturbed by all the multifold noise and rattle of the machinery, but let the noise alter in some item which, though unnoticeable to the visitor, betokens importance to the trained ear, and his passive attention is in a moment caught. The warders at an asylum have been hypnotized to sleep by the bedside of dangerous patients, and "suggested" to awake the instant the patients attempt to get out of bed, sounds which had no import for them being inhibited by suggestion. Warders in this way worked fatigue. This is akin to the repetition all day and performed night duty also for months without showing which, read by the schoolboy last thing overnight, is on waking "known by heart." Most of us can wake somewhere about a desired although unusually early hour, if overnight we desire much to do 30. Two theories of a physiological nature have been proposed to account for the separation of the complex reactions of these conditions of hypnotism from volition and from memory. R. P. H. Heidenhain's view is that the cortical centres of the hemisphere are inhibited by peculiar conditions attaching to the initiatory sense stimuli. W. T. Preyer's view is that the essential condition for initiation is fatigue of the will-power under a prolonged effort of undivided attention. Hypnotic somnambulism and hypnotic catalepsy are not the only or the most profound changes of nervous condition that hypnosis can induce. The physiological derangement which is the basis of the abeyance of volition may, if hypnotism be profound, pass into more widespread derangement, exhibiting itself as the hypnotic lethargy. This is associated not only with paralysis of will but with profound anaesthesia. Proposals have been made to employ hypnotism as a method of producing anaesthesia for surgical purposes, but there are two grave objections to such employment. In order to produce a sufficient degree of hypnotic lethargy the subject must be made extremely susceptible, and this can only be done by repeated hypnotization. It is necessary to hypnotize patients every day for several weeks before they can be got into a degree of stupor sufficient to allow of the safe execution of a surgical operation. But the state itself, when reached, is at least as dangerous to life as is that produced by inhalation of ether, and it is more difficult to recover from. Moreover, by the processes the subject has gone through he has had those physiological activities upon which his volitional power depends excessively deranged, and not improbably permanently enfeebled. (C. S. S.) MUSCOVITE, a rock-forming mineral belonging to the mica group (see MICA). It is also known as potash-mica, being a potassium, hydrogen and aluminium orthosilicate, H&KAl(SiO.),. As the common white mica obtainable in thin, transparent cleavage sheets of large-size it was formerly used in Russia for window panes and known as "Muscovy glass "; hence the name muscovite, proposed by J. D. Dana in 1850. It crystallizes in the monoclinic system; distinctly developed crystals, however, are rare and have the form of rough six-sided prisms or plates: thin scales without definite crystal outlines are more common. The most prominent feature is the perfect cleavage parallel to the basal plane (c in the figure), on which the lustre is pearly in character. The hardness is 2-2, and the spec. grav. 2.8-2.9. The plane of the optic axes is perpendicular to the plane of symmetry and the acute bisectrix nearly normal to the cleavage; the optic axial angle is 60-70°, and double refraction is strong and negative in sign. M Muscovite frequently occurs as fine scaly to almost compact aggregates, especially when, as is often the case, it has resulted by the alteration of some other mineral, such as felspar, topaz, cyanite, &c.; several varieties depending on differences in structure have been distinguished. Fine scaly varieties are damourite, margarodite (from Gr. μapyapirns, a pearl), gilbertite, sericite (from onpikós, silky), &c. In sericite the fine scales are united in fibrous aggregates giving rise to a silky lustre: this variety is a common constituent of phyllites and sericiteschists. Oncosine (from Koots, intumescence) is a compact variety forming rounded aggregates, which swell up when heated before the blowpipe. Closely related to oncosine are several compact minerals, included together under the name pinite, which have resulted by the alteration of iolite, spodumene and other minerals. Other varieties depend on differences in chemical composition. Fuchsite or "chrome-mica" is a bright green muscovite containing chromium; it has been used as a decorative stone. Qellacherite is a variety containing some barium. In phengite there is more silica than usual, the composition approximating to H2KAI3(SiO3)3. Muscovite is of wide distribution and is the commonest of the micas. In igneous rocks it is found only in granite, never in volcanic rocks; but it is abundant in gneiss and mica-schist, and in phyllites and clay-slates, where it has been formed at the expense of alkali-felspar by dynamo-metamorphic processes. In pegmatite-veins traversing granite, gneiss or mica-schist it occurs as large sheets of commercial value, and is mined in India, the United States and Brazil (see MICA), and to a limited extent, together with felspar, in southern Norway and in the Urals. Large sheets of muscovite were formerly obtained from Solovetsk Island, Archangel. (L. J. S.) MUSCULAR SYSTEM (Anatomy). The muscular tissue (Lat. musculus, from a fancied resemblance of certain muscles to a little mouse) is of three kinds: (1) voluntary or striped muscle; (2) involuntary or unstriped muscle, found in the skin, walls of hollow viscera, coats of blood and lymphatic vessels, &c.; (3) heart muscle. The microscopical differences of these different kinds are discussed in the article on CONNECTIVE TISSUES. Here only the voluntary muscles, which are under the control of the will, are to be considered. The voluntary muscles form the red flesh of an animal, and are the structures by which one part of the body is moved at will upon another. Each muscle is said to have an origin and an insertion, the former being that attachment which is usually more fixed, the latter that which is more movable. This distinction, however, although convenient, is an arbitrary one, and an example may make this clear. If we take the pectoralis major, which is attached to the front of the chest on the one hand and to the upper part of the arm bone on the other, the effect of its contraction will obviously be to draw the arm towards the chest, so that its origin under ordinary circumstances is said to be from the chest while its insertion is into the arm; but if, in climbing a tree, the hand grasps a branch above, the muscular contraction will draw the chest towards the arm, and the latter will then become the origin. Generally, but not always, a 1 For physiology, see MUSCLE AND NERVE. | muscle is partly fleshy and partly tendinous; the fleshy contractile part is attached at one or both ends to cords or sheets of white fibrous tissue, which in some cases pass round pullies and so change the direction of the muscle's action. The other end of these cords or tendons is usually attached to the periosteum of bones, with which it blends. In some cases, when a tendon passes round a bony pulley, a sesamoid bone is developed in it which diminishes the effects of friction. A good example of this is the patella in the tendon of the rectus femoris (fig. 1, P.). Every muscle is supplied with blood vessels and lymphatics (fig. 1, v, a, l), and also with one or more nerves. The nerve supply is very important both from a medical and a morphological point of view. The approximate attachments are also important, because unless they are realized the action of the muscle cannot be understood, but the exact attachments are perhaps laid too great stress on in the anatomical teaching of medical students. The study of the actions of muscles is, of course, a physiological one, but teaching. the subject has been handed over to the anatomists, and the results have been in some respects unfortunate. Until very recently the anatomist studied only the dead body, and his one idea of demonstrating the action of a muscle was to expose, and then to pull it, and whatever happened he said was the action of that muscle. It is now generally recognized that no movement is so simple that only one muscle is concerned in it, and that what a muscle may do and what it really does do are not necessarily the same thing. As far as the deeper muscles are concerned, we still have only the anatomical method to depend upon, but with the superficial muscles it should be checked by causing a living person to perform certain movements and then studying which muscles take part in them. FIG. 1.-The Rectus Mu cle of the Thigh; t show the constituent parts of a muscle. R, The fleshy belly. to, Tendon of origin. ti, Tendon of insertion. n, Nerve of supply. Artery of supply. Vein. a, v, Lymphatic vessel. P, The patella. For a modern study of muscular actions, see C. E. Beevor's Croonian Lectures for 1903 (London, 1904). Muscles have various shapes: they may be fusiform, as in fig. 1, conical, riband-like, or flattened into triangular or quadrilateral sheets. They may also be attached to skin, cartilage or fascia instead of to bone, while certain muscles surround openings which they constrict and are called sphincters. The names of the muscles have gradually grown up, and no settled plan has been used in giving them. Sometimes, as in the coraco-brachialis and thyro-hyoid, the name describes the origin and insertion of the muscle, and, no doubt, for the student of human anatomy this is the most satisfactory plan, since by learning the name the approximate attachments are also learnt. Sometimes the name only indicates some peculiarity in the shape of the muscle and gives no clue to its position in the body or its attachments; examples of this are biceps, semitendinosus and pyriformis. Sometimes, as in the flexor carpi ulnaris and corrugator supercilii, the use of the muscle is shown. At other times the position in the body is indicated, but not the attachments, as in the tibialis anticus and peroneus longus, while, at other times, as in the case of the pectineus, the name is only misleading. Fortunately the names of the describers themselves are very seldom applied to muscles; among the few examples are Horner's muscle and the oht to apolo and at auli to odgrom TRAPEZIUS Jacitoqmi pela Lox Parotid LEVATOR LABII SUPERIORIS ALAEQUE NASI LEVATOR LABII SUPERIORIS ZYGOMATICUS MINOR PLATYSMA MYOIDES 40 YET salt on all has hod Dalechainindo olimlochy Q muscles on each side of the body it will be impossible here to MUSCLES OF THE HEAD AND FACE (see fig. 2).-The scalp is moved by a large flat muscle called the occipito-frontalis, which has two muscular bellies, the occipitalis and frontalis, and an intervening epicranial aponeurosis; this muscle moves the scalp and causes the the nose has several muscles, the actions of which are indicated by their names; they are the compressor, two dilatores and the depressor alae nasi, while the levator labii superioris et alae nari sometimes goes to the nose. Raising the upper lip, in addition to the last named, are the levator labii superioris proprius and the levator anguli oris, while the zygomaticus major draws the angle of the mouth outward. The lower lip is depressed by the depressor labii inferioris and depressor anguli oris, while the orbicularis oris acts as a sphincter to the mouth. |