rygoid branch of the superior maxillary. In the upper part of the neck this nerve has a very large ganglion lying on the vertebræ, called the superior cervical ganglion. This ganglion receives branches of communication from the five upper pairs of cervical nerves, and sends off a branch to the heart. The trunk descends along the neck, and forms an inferior cervical ganglion, which has communicating filaments from the neighbouring spinal nerves, and sends several branches to the heart, forming the cardiac plexus. The sympathetic nerve then passes through the chest, over the heads of the ribs, receiving branches from each dorsal nerve, and forming a dorsal ganglion be tween every two vertebræ. In its course it sends off the splanchnic nerves, which go through the diaphragm, and form a vast and most intimate plexus about the root of the cæliac artery, called the cæliac plexus, from which the liver, pancreas, spleen, large and small intestines, and kidneys derive their nerves. All these organs receive several filaments united so as to form plexuses, and surrounding their arterial trunks. The trunk of the great sympathetic enters the abdomen, and goes over the lumbar vertebræ, receiving branches of communication, and forming lumbar ganglia; it is then continued along the front of the sacrum, where the sacral nerves supply communicating filaments, and where five sacral ganglia are formed. ORGANS OF SENSE, Organ of vision. The globe of the eye is contained in a bony socket, formed by the bones of the cranium and of the face. It is furnished with muscles which can move it in every direction, and surrounded by a very soft and delicate kind of fat, which yields to it in all its motions. It is composed of certain membranes, called its tunics or coats, and of other parts termed humours. Its figure is very nearly spherical; but the transparent portion in front is the sec tion of a smaller sphere than the globe. The optic nerve, to which the eye-ball is attached posteriorly, enters considerably on the inside of the axis of the eye. The coats of the eye are disposed concentrically; and the exterior, which is very dense, firm, and tough, is called the sclerotica. This does not cover the whole globe, but leaves a circular opening in front, filled by the transparent cornea, which, although pellucid, is a very firm and strong membrane, Hence the sclerotica and cornea together form a very complete exterior case, which defends and supports the more delicate parts within. The necessity of having the front of the globe transparent, for the purpose of admitting the rays of light, is obvious. Under the sclerotica a soft and vascular membrane surrounds the eye-ball, and is called the choroid coat. It is connected to the sclerotica by a loose adhesion, which ean be destroyed by blowing air between the membranes; but in front this adhesion is stronger, and forms a white circle, named orbiculus or ligamentum ciliare. The colour of the choroid coat is a deep brown, approaching to a black, and this colour is derived from a substance called pigmentum nigrum, which separates from the choroid by maceration, and dissolves in water so as to render it turbid, The inner surface of the choroid coat, which is universally coloured by pigmentum nigrum in the human subject, is sometimes called tunica ruyschiana; as Ruysch endeavoured to prove that it formed a distinct membrane from the external part. It is this inner surface that possesses the brilliant colours observable in animals, whence the appellation of tapetam. This surface lies in contact with the retina, but does not adhere to that membrane. On the front of the eye however, and beyond the anterior margin of the retina, the choroid is closely attached by means of numerous and very delicate folds, called the ciliary processes, to the surface of the vitreus humour, round the margin of the crystalline lens. The iris is a membrane continued transversely across the eye-ball, behind the cornea, and appearing as a continuation of the choroid from the orbiculus ciliaris. The round opening in the front of this membrane is called the pupil: it allows the passage of the rays of light into the interior of the eye. This aperture varies in its dimensions, according to the quantity of light to which the organ is exposed: a strong light causes the pupil to become contracted, in order to exclude a portion of the rays of light, which offend the organ. The aperture is dilated in a weak light, to let in as many rays as possible. Some anatomists have thought proper to employ themselves in debating at length whether these motions arise from a really muscular structure or no ; but we believe that they have not yet settled the point completely. The name of iris was applied to this part, from the diversity of colours observable in it in different individuals; and it is the colour of this that produces the colour of the eye, in the popular sense of the phrase. There is a remarkable correspondence in this point between the skin and hair and the iris. A light complexion and hair is accompanied with blue, grey, or the lighter colours of the iris; while a dark skin and black hair are attended with the dark brown iris. In that curious variety of the human race, called the Albinos, where the skin and hair are of a dead milk-white hue, in consequence of a total absence of the rete mucosum or colouring principle, the colouring matter of the iris and choroid is also deficient, and these parts appear red from the numerous blood-vessels which they contain. The posterior surface of the iris is covered by pigmentum nigrum, and is called the uvea. Under the choroid coat is found a third membrane of the eye-balls, called the retina, which is formed by the expansion of the medullary substance of the optic nerve, and forms the immediate organ of vision. It is of a yellowish grey colour, and so extremely soft as almost to be lacerated by the slightest touch. Its outer surface is entirely unconnected with the choroid coat; and the inner surface is expanded on the vitreous humour, but not connected to it. It terminates in front by a distinctly defined edge, where the ciliary processes begin to adhere to the vitreous humour. On the inside of the retina are seen the branches of an artery. and vein, which enter through the centre of the optic nerve, (arteria et vena centralis oculi). The part at which it enters the eye is termed the porus opticus, and is of course insensible; and hence physiologists have explained the reason why the optic nerve is inserted out of the axis of the eye; as otherwise the axis of vision would have fallen on an insensible part of the retina. On the outer, or temporal side of the retina, there is a fold of the membrane of a bright yellow colour, in the recent state, and there is also said to be an aperture. These circumstances were first pointed out by Soemmerring, and have been named after him. The vitreous humour occupies the greatest share of the globe of the eye. It consists of a clear water contained in a cellular substance, which is so perfectly transparent as to resemble pure glass, whence its name is derived. The cellular substance is con densed on the surface into a smooth membrane, called the membrana hyaloidea. This is marked in front by a circular series of black radiated lines, caused by the adhesion of the ciliary processes, which, like other parts of the choroid, are covered with pigmentum nigrum. Under these a circular canal runs, named the canal of Petit. The crystalline humour or lens is imbedded in the front of the vitreous humour. Its size is about that of a pea, but it is much more flattened in form. It is of a waxy consistence, softer externally, and growing gradually firmer towards the centre. The lens is contained in a capsule, formed by the membrana hyaloidea, splitting into two layers. It has no apparent connection to this capsule. It is an opaque state of this body that constitutes the disease called cataract. The aqueous humour is a small quantity of transparent water, placed immediately behind the cornea, and occupying the space between that membrane and the crystalline lens: it is easily reproduced when let out. In the midst of the space occupied by this humour the iris is found, and it divides the space into two portions, called the anterior and posterior chambers of the eye; which communicate by means of the pupil. The anterior is much the largest of these. The choroid coat, ciliary processes, and iris are very vascular, and derive their supply from the ciliary branches of the ophthalmic artery. The iris is very largely supplied with nerves from a small ganglion, named lenticular, formed on a branch of the nervus motor, or nerve of the third pair. These are called the ciliary nerves. Of the eye-lids and lacrymal apparatus.-The eye-ball is covered by two moveable curtains, formed by a folding of the cammon integument, and called the eye-lids. In order to keep these uniformly expanded, and to prevent them from forming wrinkles, each of them contains a thin portion of cartilage, adapted in figure to the convexity of the globe, and called the tarsus. In order to provide still further for the greatest possible facility of motion, the eye-lids are lined by a smooth and polished membrane, and the globe of the eye is covered by the same membrane, on its anterior part: this is called conjunctiva, as it serves to connect the front of the eye-ball to the eyelids. The junctions of the eye-lids are called the internal and external canthus, or angle of the eye. They are opened by the levator palpebræ lifting up the upper lid; and this muscle is in a state of constant action so long as we keep our eyes open. They are closed by the circular orbicularis palpebrarum. The cilia, or eye-lashes, are two rows of strong curved hairs implanted in the opposed edges of the two eye-lids, and admirably calculated for protecting the eye from dust or other foreign bodies. The hairy prominences above the eye-lids are the supercilia, or eye-brows; these are very moveable; they serve as a protection to the eyes, and are much concerned in expressing the passions. The lacrymal sac is a small membranous bag, placed in the hollow formed at the inner edge of the orbit. The tendon of the orbicularis palpebrarum, which generally forms a slight eminence visible through the skin, crosses the middle of this bag. A canal, called the ductus nasalis, and lodged in a groove of the superior maxillary bone, conveys the tears into the nose, where it terminates by an open orifice within the inferior turbinated bone. ORGAN OF HEARING. This organ is divided into two parts, the external and internal ear, by the membrana tympani. The situation of the former on the outside of the head is well known; the latter is contained in the petrous portion of the temporal bone. The external ear consists of two parts, viz. the pinna, or ear popularly so called, and a tube called meatus auditorius externus, leading from the pinna to the membrana tympani. These parts serve for collecting sounds, and conveying them to the membrana tympani. In order to facilitate the motions of the eye-lids and eye balls on each other, the surface of the conjunctiva is constantly moistened by a watery and mucilaginous fluid poured out by the arteries of the part. The incrustations of the mucilage in the night would glue the eye-lids together; but this effect is obviated by a natural ointment formed in a very elegant glandular apparatus on the inner surface of the tarsi. We The pinna consists of a convoluted cartithere find about 16 or 17 longitudinal paral-lage inclosed by common integuments. The lel rows of very minute glandular bodies; and these pour out their sebaceous secretion from a series of apertures on the edges of the eye-lids. They are called the meibomian glands, and ciliary ducts. The fluid just described is constantly formed on the surface of the conjunctiva; but on extraordinary occasions, as when an irritating foreign body is in the eye, or in consequence of affections of the mind, a fluid is poured out in greater abundance, which has the name of tears, and is secreted by the lacrymal gland. This is a small conglomerate gland, situated in the orbit, near the upper eye-lid, and having ducts which terminate on the surface of the conjunctiva; but which, on account of their minuteness, are hardly demonstrable in the human subject. The utility of this secretion in washing away any foreign substance must be sufficiently obvious. The superfluous part of the lacrymal secretion is conveyed through two very fine tubes to a small bag, situated at the internal angle of the eye. These tubes commence by open mouths, called the puncta lacrymalia, from the inner extremities of the eye-lids, and are about equal in size to admit a hog's bristle. There is a little fleshy projection at the corner of the eye, and between the two puncta, called caruncula lacrymalis. lower part, which is pierced for ear-rings, has no cartilage, and is called the lobulus. The helix is the fold forming the external circumference of the ear; the next eminence to this, which forms the margin of the great cavity of the external ear, is called anthelix; it separates at its upper and anterior end into two processes, named crura. The projection immediately in front of the meatus is the tragus, and that immediately opposite, the antitragus. The great cavity within the anthelix, and leading to the meatus, is called the concha. Several sebaceous glands are situated in the folds of the ear. The meatus externus is formed first by a portion of cartilage, continued from the pinna, and more interiorly it consists of a canal in the substance of the bone. This bony part does not exist in the fœtus, where the meatus is wholly cartilaginous. The common integuments continued from the pinna line the meatus externus, and the cuticle is produced over the membrana tympani. The surface of the meatus at its commencement is furnished with numerous fine hairs, and the canal is moistened by a secretion of an oily and inflammable nature, called cerumen. This is produced by numerous small glands, visible on the external surface of the meatus, and distinguishable by their yellowish colour. The cerumen concretes, and is collected sometimes in such quantity, as to induce a slight degree of deafness, which is easily removed by syringing with warm water. The membrana tympani, which is a circular membrane above a quarter of an inch in diameter, is stretched across the inner extremity of the meatus, and derives its name from a comparison with a drum head, to which it bears some analogy in its use. In the foetus it is stretched on a distinct bony ring, called the annulus anditorius. This ring is deficient at its upper part, and has no bony union to the rest of the temporal bone, but it becomes united soon after birth. This membrane is concave on its exterior surface, and convex towards the tympanum. Its position is inclined, the upper margin being more towards the outside of the head, and the under part farther inwards; so that the superior part of the meatus forms an obtuse angle, and the inferior part an acute angle with the membrane. The internal ear consists of two divisions, riz. the tympanum and the labyrinth. The tympanum is an irregular bony cavity, which will about admit the end of a finger, hollowed out of the temporal bone, just-within the membrana tympani. It has several communications with the neighbouring parts. Opposite to the membrana tympani are two openings, which lead to the labyrinth of the ear. The upper one is named the fenestra ovalis, the lower one the fenestra rotunda, and the projection between them is called the promontory. The fenestra ovalis is filled, as we shall presently see, by one of the little bones of the tympanum, and the fenestra rotunda is closed by a membrane. The eustachian tube, or iter a palato ad aurem, opens in front of the tympanum. It commences by an expanded cartilaginous orifice at the back of the nostrils, passes through the substance of the temporal bone, and terminates by a contracted orifice in the tympanum. Its office is to convey air into the cavity of the tympanum. The membrana tympani is thrown into vibrations by the impulse of the sonorous undulations of the air, and that vibration could not take place unJess there was air in the inside as well as on the outside of the membrane. Water, or any other fluid, would not have answered the purpose. Hence an obstruction of this tube causes deafness, which surgeons have attempted to remedy by puncturing the membrana tympani. An opening in the latter membrane of a small extent does bý no means injure hearing; for many persons have the power of impelling tobacco smoke, or agitating the flame of a candle through the ear, and yet seem to have a perfect use of the organ. In these cases the air or smoke çnters the eustachian tube from the throat, and passes through the unnatural aperture in the membrane. The mastoid process of the temporal bone is composed internally of numerous cells, communicating with each other, and finally opening into the back part of the tympanum. These do not exist in the fœtus. The cavity of the tympanum contains a chain of small bones, called ossicula auditus, connected by one end to the membrana tympani, and by the other to the fenestra ovalis. Of these the first, which is compared to a hammer, is called the malleus; the second is named the incus, and the third the stapes. The malleus possesses a manubrium, or handle, a long and short process, and a head which forms an articular surface. The incus resembles a grinding tooth, with its two fangs diverging. We remark in it a body, the surface of which is hollowed out to receive the head of the malleus; a long and a short leg. The stapes has an exact resemblance to the iron part of a stirrup ; it has a head, two crura, and a basis. The handle of the malleus is firmly connécted to the membrana tympani; and hence arises the external concavity and inhead of that bone is joined to the body of ternal convexity of the membrane. The the incus, whose long leg is articulated to the head of the stapes. The basis of the stapes fills up the fenestra ovalis. The ends of the bones forming these articulations are covered with cartilage, and furnished with capsules like other joints. The bones of the tympanum have some small muscles connected to them, by which they are moved outwards, or towards the membrana tympani, and inwards, or towards the fenestra ovalis. The first of these motions relaxes, the latter stretches the membrane. The names of these muscles are, tensor tympani, laxator tympani, and stapedeus. The nerve called chorda tympani passes across the tympanum, between the handle of the malleus and the long leg of the incus. The use of the ossicula auditus seems to be that of transmitting the vibrations of the air from the membrana tympani to the labyrinth. The final use of the muscles which moves these bones is unknown. The labyrinth of the ear consists of three parts:-1. A spiral bony canal, twisted like a snail-shell, and thence called the cochlea. 2. Three semicircular bony canals: and 3. A small cavity, called the vestibulum, into which the cochlea and the semicircular cana's open. These parts are formed of the hardest bone in the body, almost equal in solidity to ivory, and the petrous portion of the temporal bone, which incloses them, is of a similar structure. In the fœtus the labyrinth is surrounded by a softer and looser kind of bone, so that it can be most easily dissected at that age. The vestibulum is about equal in size to a large pea, and the fenestra ovalis opens into the middle of the cavity. It has also five openings from the semicircular canals; the superior and exterior joining by one of their extremities, and opening by a hole. common The cochlea has two turns and a half. Its canal turns round a bony centre, called the modiolus, to which is attached a thin plate of bone, projecting into the cavity of the cochlea, and named lamina spiralis. This projecting plate divides the canal of the cochlea into two parts; one opening into the vestibulum, the other at the fenestra rotunda. The latter is called the scala tympani, the former scala vestibuli. The vestibulum, cochlea, and semicircular canals are lined by a delicate vascular membrane, on which the portio mollis of the şeventh pair of nerves is distributed. This membrane contains a clear water. The filaments of the auditory nerve pass from the meatus auditorius internus through a number of very small apertures, which lead to the labyrinth, and they terminate on the vascular membrane of the labyrinth, so that the nervous pulp is exposed almost bare to the contained fluid. The distribution of the nerve on the cochlea is particularly beautiful. The aqueducts of the ear are two very fine tubes passing from the vestibulum and cochlea to open on the surface of the dura mater. ORGAN OF SMELLING, The nose is a cavity of very irregular figure, formed chiefly by the bones of the face, and communicating with the various sinuses or bony cells formed in the head. It is separated from the brain above by the cribriform lamella of the ethmoid bone. This separation is a perfect one, and the two cavities of the cranium and nose are wholly distinct from each other, although they are supposed by the uninformed in anatomy to communicate together. The bottom of the cavity is formed by the upper surface of the palate, The general cavity is divided into two equal halves, called nostrils, by the septum narium, a thin and flat bony partition descending from the cribriform lamella to the palate. The flat surface of the septum may therefore be said to form the inner side of the nostril; and its outer side presents three bony eminences, called the conchæ narium, or turbinated bones. Moreover, the following excavations or sinuses open into the cavity at various parts, Two frontal sinuses; numerous cells of the ethmoid bone; two sphenoidal sinuses; and two great hollows in the upper jaw bone, called the antra, or maxillary sinuses. The front openings of the nostrils are well known. This aperture is heart-shaped in the skeleton, the broadest part being towards the mouth; but it is much altered in the recent subject by the apposition of pieces of cartilage, the broadest of which are the lateral portions termed alæ nasi. Behind, the nostrils open by large apertures into the upper and anterior part of the pharynx, above the velum pendulum palati. The sides of the bony cavity just described are covered by a thick, soft, and very vascular membrane, called membrana schneideriana, or pituitaria. Its surface is constantly moistened by a secretion of mucus from the arteries, with which it is very copiously supplied. This prevents the effects which the current of air in respiration would otherwise produce, of drying the membrane. It is only an increased quantity of this secretion, altered too somewhat in its quality, that is discharged from the nose in colds, and which is popularly supposed to come from the brain. This membrane extends into the cells which communicate with the nose, but is thinner and less vascular there. The ethmoidal cells open into the cavity of the nose, partly above, and partly under the loose edge of the superior turbinated bone. The frontal sinuses open into the front of these cells; and the sphenoidal sinuses into the back part of them. The antrum maxillare has a round opening between the two turbinated bones. The nasal duct opens under the inferior of these bones: and the expanded orifice of the eustachian |