« PreviousContinue »
other. The marrow occupies the tube left in the middle of the long bones, and also fills the cancelli of their extremities. The cellular substance, which contains the marrow, being condensed upon the inside of the walls of the bone, and adhering to them, has been termed the periosteum internum.” We observe in the principal bones arteries, much larger than those which nourish the bone, penetrating these bodies obliquely, and spreading their branches upon the medullary cells. Various unsatisfactory opinions have been proposed concerning the use of the marrow. The utility of the bones being formed as they are, small and tubular in the middle, expanded and spongy at their extremities, has been already explained. If then spaces are necessarily left in their interior parts, those spaces must be filled with something; for they cannot be left void, or the immense pressure of the atmosphere would crush their sides, and destroy the vacuum. There is no matter in the animal body more suitable to fill their spaces than the marrow; and it is to be regarded as a part of the adipous system of the animal. From the circumstances which have been detailed in the foregoing account, viz. the great and general vascularity of bones; the quantity of soft substance existing in every part of them; their growth and mutation of form in disease, &c. it is natural to conclude, that there exist in the composition of every bony fibre, arteries for its formation, absorbents for its removal, cellular substance for the connexion of its parts, and nerves to give animation to the whole. In this view of the subject, we see no essential difference of structure between bones and other parts of the body; nor do we expect any essential difference in the functions of their nutrient and other vessels. We naturally conclude that bony fibres are formed and repaired, and that they undergo mutation and removal in the same manner, and from the same causes that soft parts do.
is a semipellucid substance, of a milk-white or pearly colour, entering into the composition of several parts of the body. It holds a middle rank, in point of firinness, between bones or hard parts, and the softer constituents of the human frame. It appears, on a superficial examination, to be homogeneous in its texture : for, when cut, the surtace is uniform, and contains uo visible cells,
cavities, nor pores; but resembles the section of a piece of glue. It possesses a very high degree of elasticity; which property distinguishes it from all other parts of the body. Hence it enters into the composition of parts, whose functions require the combination of firmness with pliancy and flexibility: the preservation of a certain extermal form, with the power of yielding to external force or pressure. Cartilages are covered by a membrane, resembling, in texture and appearance, as well as in its office, the periosteum of bones: this is termed the perichondrium. They receive arteries and veins from this membrane: these vessels, however, have never been demonstrated in the cartilaginous crusts of articular surfaces. Absorbent vessels cannot be actually shewn, but their existence is abundantly proved by many phenomena. The conversion of cartilage into bone is alone sufficient for this purpose. The cartilaginous substance is gradually removed, as the formation of the bone advances. In affections of the joints, their cartilaginous coverings are often both entirely destroyed, or partially removed; which appearances can only be ascribed to the action of absorbent vessels. It does not seem to possess nerves, as it is entirely destitute of sensibility. The thinner cartilages of the body are resolved by maceration into a kind of fibrous substance: e.g. those of the organs of sense. Those of the ribs are found by long maceration to consist of concentric oval laminae. In some there are tendinous fibres intermixed; as in those of the vertebrae. Anatomists divide cartilages into two kinds: the temporary and the permanent. The former are confined to the earlier stages of existence; the latter commonly retain their cartilaginous structure throughout every period of life. The temporary cartilages are those in which the bones of the body are formed. They are hence called by the Latin writers ossescentes. All the bones of the body, except the teeth, are formed in a nidus of cartilage. The form of the bone, with its various processes, is accurately represented in these cartilaginous primordia; and it is the substance alone which changes. The permanent cartilages are of various kinds. We find them composing the external ear, external aperture of the nostrils, and eye lids. The larynx is entirely composed of this substance; and the trachea,
with its branches, is furnished with cartila. ginous hoops, by which these tubes are kept permanently open, for the ready passage of air to and from the lungs. The bodies of the vertebrae are joined by large masses of a peculiar substance, partaking of the properties and appearance of cartilage and ligament; which allow of the inotions of these parts on each other, without weakening the support that is afforded to the upper parts of the body in general, and to the head in particular, by the vertebral column. These cartilages impart a great elasticity to the spine; by which the effects of concussion from jumping, from falls, &c. are weakened, and destroyed, before they can be propagated to the head. When the body has been long in an erect position, the compression of these cartilages, by the superior parts, diminishes the height of the person. They recover their former length, when freed from this pressure: hence a person is taller when he rises in the morning, than after sustaining the fatigues of the day, and the difference has sometimes amounted to an incl. Cartilages are sometimes interposed between the articular surfaces of bones; where they fill up irregularities, that might otherwise impede the motions of the part; and increase the security of the joint, by adapting the articular surfaces to each other. The articular surfaces of bones are, in every instance, covered by a thin crust of cartilage, having its surface most exquisitely polished, by which all friction in the motions of the joint is avoided, and the ends of the bones glide over each other with the most perfect facility. Nomenclature of bones.—The processes or apophyses of bones bear different names according to their figures. Hence we find them described under the terms of head (roundish ball); condyle (a flattened head); neck; tuberosity; spine; &c. others have particular names from supposed resemblances. The cavities or depressions of bones are called cotyloid, when deep; glenoid, when shallow. Again, we have pits, furrows, notches; sinuosities, fossae, sinuses, foramina, and canals. Connection of bones.—Anatomists have divided these into three classes; Symphysis, Synarthrosis, and Diarthrosis. The term symphysis merely denotes the union of the conjoined bones, without any reference to peculiar form or motion; hence it is divided, according to the means by which it is effected, into.
1. Synchondrosis, where cartilage is the connecting medium: this is exemplified in the junction of the ribs and sternum; of the bodies of the vertebrae; and of the ossa pubis: 2. Synneurosis or syndesmosis; where ligaments are the connecting bodies, as in all the moveable articulations: 3. Syssarcosis; where muscles are stretched from one bone to another. The synarthrosis, or immoveable conjunction of bones, consists of, 1. Suture; where the bones are mutually indented, as if sewn together: 2. Harmonia; where the conjunction is eflected by plane surfaces. 3. Gomphosis; where one bone is fixed in another, as a nail is in a board. The teeth afford the only specimen. Diarthrosis, or moveable conjunction of bones. The conjoined parts of the bones are covered with a smooth cartilage, and connected by one or more ligaments. It has three subdivisions; viz. 1. Enarthrosis, or ball and socket ; where a round head of one bone is received into a cavity of another, and consequently is cap ble of motion in all directions; 2. Arthrodia; where the cavity is more superficial, and much motion not allowed; 3. Ginglymus ; where the motions are restricted to two directions, as in the hinge of a door. The skeleton consists of an assemblage of all the bones in the body, excepting the os hyoides. It is said to be a natural skeleton, when the bones are connected by means of their own ligaments or cartilages; an artificial one, when wire or other extraneous substances are employed. It is divided into the head, trunk, and extremities. The head consists of the cranium and the face. The former of these parts consists of 1 or 2 ossa frontis; 2 ossa parietalia; 1 os sphenobasilare; 2 ossa temporum; 2 mallei; 2 incudes; 2 stapedes; and 1 os aethmoideum ; on the whole, of 13 or 14 bones. The face has 2 ossa maxillaria superiora; 2 ossa palati; 2 ossa mala: ; 2 ossanasi; 2 ossa lacrymalia; 2 ossa turbinata inferiora; 1 os vomer; 1 maxilla inferior; 32 teeth; on the whole, 46 bones. The tongue has 5 ossa lingualia. The bones of the head are therefore 53 or 60 ; with the lingual bones 64 or 65. In the neck there are 7 cervical vertebrae; in the chest 12 dorsal vertebrae, 24 ribs; 2 or 5 bones of the sternum: in the loins 5 lumbar vertebrae; in the pelvis 1 sacrum, 1 ossa coccygis, 2 ossa innominata. Therefore the whole trunk has 57 or 58 bones. The shoulders have 2 clavicles and 2 scapula; the arms 2 humeri; the fore-arms 2 ulnae and 2 radii; the wrists 2 ossa navicularia; 2 ossa lunata; 2 ossa cuneiformia; 2 ossa orbicularia; 2 ossa trapezia; 2 ossa trapezioidea; 2 ossa capitata; 2 ossa unciformia: the metacarpi 10 metacarpal bones: the fingers 10 posterior phalanges; 8 middle phalanges, 10 anterior phalanges, and 8 sesamoid bones. --The bones of the upper extremities are in the whole 72. The thighs have 2 femora: the legs 2 tibias, 2 patellae, and 2 fibulae: the tarsi 2 astragali, 2 ossa calcis, 2 ossa navicularia, 6 cuneiform bones, 2 ossa cuboidea: the metatarsi 10 metatarsal bones: the toes 10 posterior phalanges, 8 middle phalanges, 10 anterior phalanges, and 6 sesamoid bones. The bones of the lower extremities are 66. The whole skeleton contains 259 or 261 bones. Of the bones just enumerated, the os frontis, spheno-occipitale, ethmoideum, vomer, inferior maxilla, the vertebræ, sacrum, and os coccygis, the bones of the sternum, and the os linguale medium, are single bones; and being placed in the middle of the body, are consequently symmetrical. Of all the other bones, there is a pair consisting of a bone for the right, and another for the left side. The structure of the whole skeleton is therefore symmetrical; since an imaginary perpendicular line drawn through the whole would divide even the single bones into a right and a left half exactly resembling each other. This observation must however be taken with some allowance; since the corresponding bones of one side are not always perfectly similar to those of the opposite; nor do the two halves of the single bones always exactly agree in form, &c. The entire natural skeleton of a man of middle stature, in a dried state, weighs from 150 to 200 ounces; that of a woman from 100 to 160 ounces. Bones of the head.—The cranium is the oval bony cavity containing the brain; the face is placed at the anterior and lower part of this cavity, and holds some of the organs of sense, and the instruments of mas. tication.
The bones of the head are joined by sutures, a mode of union nearly peculiar to themselves; hence, when all the soft parts are destroyed by maceration, they still remain most firmly connected to each other, excepting the front teeth and the lower jaw. The sutures are formed by numerous sharp and ramified processes of the opposed edges of the different bones, shooting into corresponding vacuities of each other. In some instances, however, the bones seem to be joined by the opposition of plane sur. faces, and here the union appears externally like a mere line, instead of the irregular zigzag course, which it takes in the former case. The last mentioned junction is called harmonia. In the foetal state, the bones of the cramium do not touch each other, but are separated by considerable intervals of membrane, and have thin extenuated margins, which allow them to ride over each other when subjected to pressure. The larger and more conspicuous of these intervals are called fontanelles, and allow of the pulsation of the brain being felt in a young subject. The importance of this structure, in allowing the head to accommodate itself to the varying figure of the parts, through which it passes in the act of parturition, and to sustain the violent pressure, which it experiences in the same act, is sufficiently obvious. In the progress of ossification the edges of the bones meet each other, and become united by the sutures. The use of these in the adult cranium, cannot be satisfactorily asssigned ; nor do we see any difference that would arise, if the head had been composed of one piece only, without any suture. In old persons the sutures often become more or less generally obliterated. The individual bones are very firmly connected by this mode of union. The edges of the different bones overlap each other at different parts, so that they are mechanically locked together, and cannot be driven in by any force ab erterno. The bones of the cranium are composed of two plates of compact bony substance, called the external, and internal or vitreous tables; and an intervening more or less ob. vious reticular texture termed diploe. The proportion of these constituent parts varies very considerably; the diploe is in no case of a very loose or open texture. The thickness of individual skulls is subject to great variety; and there is much difference in the various parts of the same skull. For the internal surface is every where exactly
moulded to the form of its contents, instead of influencing them, as we might have expected a priori. Hence the convolutions of the brain, the vessels, which ramify on its surface, &c. all leave prints on the inner table. The ordinary thickness varies from about the fifth of an inch to almost a mere line. The common number of the bones of the cranium is, as we have already stated, 7; but this is often increased by small portions formed between the others, and surrounded by distinct sutures. These are called ossa triquetra, or wormiana. The form of the cranium is elliptical, and pretty regularly so, particularly on the front, upper and back part, and sides. The smaller circle of the ellipse is in front, and the larger behind. It is tolerably smooth extermally, except its basis, and it is almost entire or unperforated, except at the same part. In thissituation, however, it possesses numerous holes, or as they are technically named, foramina, which transmit blood-vessels to the brain, and the nine pairs of nerves, which arise from that organ. The upper and lateral parts of the cranium constitute a bony vault or arch, for protecting the brain; this part is distinguished by the name of the skull cap. Individual bones of the head.—The os frontis forms the upper and anterior part of the skull; the eyebrow, and the roof of the orbit. The ossa parietalia are called also ossa bregmatis, since the fontanelles or bregmata are formed between their edges. They compose the whole upper and most of the lateral parts of the skull; and possess an irregularly quadrangular figure. The ossa temporum compose the lower part of the sides, and the middle of the basis of the cranium. They are divided into a squamous portion, a mamillary, and a petrous portion. The former of these has a process contributing to the zygoma, or bony arch, at the side of the cranium, under which the temporal muscle passes. The second is also remarkable, by forming a large nipple-like protuberance towards the basis cranii. The third, which projects into the cavity of the skull, contains the organ of hearing. The os spheno-occipitale has generally been described as two bones. The occipital portion forms the posterior portion of the basis cranii, and a part also of the back of the bony case. The sphenoid portion is situated in the middle of the base of the skull, and extends
across it from one temple to another. It is extremely irregular in its figure, and divided into a body placed in the middle, two alae on the sides, and two pterygoid processes projecting downwards. The os ethmoides occupies the middle of the forepart of the basis cranii. It lies in the interval between the two orbits, and contributes to the cavity of the nose. It consists of an irregular assemblage of bony cells, and processes of a very thin and delicate formation. It has a cribriform or horizontal plate towards the brain; a nasal or perpendicular plate; 2 turbinated bones; cells; and two orbital plates. The sutures joining these are the coronal, between the os frontis and the two ossa parietalia; the sagittal, between the two ossa parietalia; the lambdoidal, joining the ossa parietalia to the os occipitis; the squamous, between the temporal and parietal bones. The foramina occurring in the cranium, for the transmission of nerves are; 1, those of the cribriform plate of the ethmoid bone: 2, f. optica: 3, f. lacera orbitalia: 4, f. rotunda: 5, f. ovalia: 6, meatus auditorii intermi: 7, f, lacera in basi cranii: 8, f. condyloidea anteriora: 9, foramen magnum. Those which transmit blood vessels are; 1, canales carotici: 2, f. spinosa: 3, f. lacera in basi cranii: 4, f magnum. Bones of the face.—The ossa nasi constitute the arch of the nose. The ossa lacymalia or unguis are placed at the forepart of the inner edge of the orbits, and contain an excavation which holds the lacrymal bag. The ossa malarum form the prominences of the cheeks. The ossa maxillaria superiora form the largest portion of the upper jaw, and most of the bony palate, or roof of the mouth; they contain also the upper teeth. The ossa palati form the back part of the bony palate. The ossa turbinata inferiora are situated in the cavity of the nose.The former completes, with the nasal portion of the ethmoid, the septum that divides the two mostrils. The maxilla inferior is articulated to the basis cranii, and holds the lower teeth. The bones of the cranium and face compose the two orbits, or pyramidal bony cavities, holding the organs of vision; to each of these, seven bones contribute. They also form the cavity of the nose, which is very extensive, and includes portions of nearly all the bones of the face, and some of the skull. It has various cells, formed in the bones of the skull and face, opening into it.
The teeth.-These organs are composed internally of a very hard bony substance; and are covered externally by a still harder matter, called the cortex or enamel.Each tooth has a body or crown, which is the part seen in the mouth; a neck, round which the gum adheres; and one or more fangs or roots, which are sunk in a process of the jaw, called the alveolar. These bodies are not formed in a nidus of cartilage, like bones, but on a soft vascular body, called a pulp, which may be compared to the core, on which a horn is formed. This is surrounded by a delicate membrane called the capsule of the tooth. When the teeth are being formed, these pulps and capsules with the rudiments of the teeth, are lodged in cavities hollowed out of the jaw-bone. They afterwards rise, and, piercing the gum, appear in the mouth. Teeth differ from other bones in possessing no vessels nor nerves in their substance. As they are destined for the merely mechanical function of triturating the food, such parts would not have been suitable to this office. The pain of tooth-ach arises from a nerve, which, with a vessel, resides in a 'hollow, formed in the centre of the fang and body of each tooth. These parts are exposed by the decay. The teeth, in consequence of possessing no vessels, are only affected by chemical and mechanical causes. They do not repair the effects of trituration, nor of accidental injury; nor do they suffer from any of the diseases, which affect other bones. There are two sets of teeth; the first are fewer in number, and smaller in size; as they fall out at a certain age, to make room for other larger ones, they are called deciduous or temporary. The second set lasts throughout life, and are called the adult or permanent set. The latter consists of 32 teeth; 16 in each jaw. There are four incisores or cutting teeth in front; 2 canini or cuspidati, or dog teeth, placed one on each side of the former; 4 bicuspides behind the last; and 6 molares behind these. From the late period at which the last molaris appears, it is called the dens sapientiae, or wise tooth. The temporary set consists of twenty teeth; ten in each jaw. There are 4 incisores; 2 cuspidati; and 4 molares. The permanent teeth are lodged at first in cavities of the jaw, near the roots of the temporary ones; and as these last are shed, rise up to supply their places. The bone of the tongue is called os
hyoides from its very accurate resemblance
to the Greek v. It consists of a body, two cornua, and two appendices, which are in fact so many separate bits of bone. The bones of the trunk consist of those of the spine, thorax, and pelvis. The spine consists of twenty-four true or moveable vertebrae; an os sacrum, and an os coccygis (which indeed is composed of four pieces): these last bones bearing considerable resemblance to the vertebrae, are called sometimes the false vertebrae. Each vertebra has a body, which is situated anteriorly, and consists of a cylindrical piece of bone; a perforation behind this, in which the spinal morrow runs; two superior and two inferior articulating processes, by which it is joined to the bone immediately above and below it; two transverse processes, and one spinous process, which projecting behind, forms a sharp ridge, from which the name of spine has been applied to the whole column. The vertebrae are divided into three classes, according to their situation: the seven upper ones are called cervical: of these, the first, that immediately supports the head, is called the atlas; and the second, from a remarkable bony process which it possesses, the vertebra dentata. The twelve next are called dorsal vertebrae, and are distinguished by having the ribs articulated to them. The five last are called lumbar. These all differ from each other in some circumstances. The most obvious distinction arises from the size: the upper ones are the smallest, and there is a gradual increase as we descend. The column of the spine, when viewed altogether, is not perpendicular; it stands forwards in the neck, recedes in the upper part of the back, and projects again in the loins. Holes are left between the bones for the transmission of the nerves which arise from the spinal marrow. The sacrum forms the back of the pelvis, and is hollowed out in front. In form it is triangular, and the base is joined to the last vertebra. It is perforated by a canal, in which the termination of the medulla spinalis is lodged. Its apex has connected to it the os coccygis. The thorax is formed by the twelve dorsal vertebrae, the ribs, and sternum. The ribs are long, curved, flattened, and narrow bones, attached behind to the dorsal vertebra, both in their bodies and transverse processes, and joined in front to a piece of cartilage. They are twelve in number, and the seven upper ones, whose cartilages are affixed to the sides of the sternum, are called true ribs; the five lower ones, the cartilages