also the majority of their processes, are separated from the body by a layer of cartilage; they will therefore be considered with the process of ossification. The apophyses or processes are divided into articular and non-articular. The first are modified according to their forms; the beads when they approach more or less to the hemispherical shape; if they are elongated, they are termed condyles; and when they have the form of teeth, they are called eminences or dentations. <Callout type="important" title="Important">The non-articular processes are eminences which vary very much in their form and size.</Callout> Some of them project considerably from the surface of the bones, and are named from their supposed resemblance to certain bodies, from their relative position, or from their uses. Thus there are processes which are called coronoid, mastoid, styloid, coracoid, spinous, odontoid, transverse, orbitary, mechanteric, &c.
The cavities of the bones are, like the projections, divided into articular and non-articular. The articular cavities are of various depths and forms; those which are deep with large brims, are named cotyloid, while those which are superficial are called glenoid cavities. When the depression has the form of a pulley, it is termed trochlea; and, lastly, the cavities which axe conical, are called alveoli.
<Callout type="risk" title="Risk">The non-articular cavities are very numerous, as they are met with in all parts of the bones.</Callout> Some of them completely pass through the bones; others penetrate deeply into their substance; and several are confined closely to the surface, and are consequently superficial. Those of the first species are called foramina, or holes, if they pass through a thin bone, and canals or conduits if their passage is of greater extent, it frequently happens that two or more bones are united to form a foramen or canal; as, for example, the foramen lacerum basis cranii posterius, and canalis palato-maxillaris. These holes and passages are provided for the transmission of soft parts, especially for vessels and nerves.
The cavities which penetrate deeply but do not pass through are of two kinds; those of the first class are formed in the substance of the bones, and, having small apertures, they are called sinuses; or, if they are divided into several spaces, they arc termed cells; they ore all lined with mucous membrane, and are filled with air. The cavities of the second class are formed for the transmission of vessels, which are fitted for the nourishment of the bones. They are of various size, and may be referred to three varieties. 1. In the long bones they form canals, which communicate toward the middle of the substance, by an opening which is called the medullary foramen; they slant obtusely into the interior, or cancellated structure; the large irregular bones, as the ossa innominata, possess similar canals. 2. The ends of the long, and the surface of the short bones, have numerous openings, which lead to their internal spongy texture; we may judge of their number from the ext, that Bichat counted one hundred and forty on the inferior extremity of the femur, and fifty on the os calcis. 3. The third species of nutritive passages consists of a great number of minute pores, which can be seen with the naked eye on the surface of the compact structure; the blood-vessels which enter those openings, and also those of the second class, are derived from the periosteum; but the arteries of the medullary foramina are distinct from the fibrous membrane, having their origin in some of the large neighboring vessels.
The superficial cavities are numerous, and of diverse forms. Those which are larger at their orifices than at their bottom, are called fossae; they are intended for the reception of glands, as the submaxillary and lacrymal glands; depressions; some arc formed for vessels and these an: termed furrows, grooves, &c.; others for tendons. The bones are strongly marked in the male skeleton, the various processes being large and developed, and the cavities distinct and well defined; this strength of the male corresponds with the fulness and power of the muscular system, with which they are so inseparably connected.
<Callout type="tip" title="Tip">The skeleton of the female, on the contrary, is more delicately framed; the bones are small and lightly made; the processes are but little prominent, so that there is an absence of that asperity and inequality which arc so strongly characteristic of the skeleton of the male.</Callout> There are also differences which relate to the important function of generation. Thus the clavicle is short, the lumbar portion of the spine is elongated, and the pelvis especially, is very capacious; all these modifications in the dimensions of the trunk, are evidently intended to increase the size of those cavities which receive the impregnated womb.
Section IV. Mechanical Texture of Bone. Non-muscular strength has been an object of anatomists for a long period directed to the investigation of the texture of bone, there is at the present day considerable difference of opinion on this subject. Malpighi is usually considered as the first who threw any light on the intimate structure of these organs. He discovered that their basis consists of an animal matter, which has been proved, by recent experiments, to be cellular very much condensed. In this cells and arteries of this substance, a quantity of earthy matter is lodged, which was noticed by Herissant nearly one hundred years ago; although the chemical nature of it was but little understood until about forty years since.
In order to examine the osseous tissue, it is necessary, on account of its extreme hardness, to prepare the bone by steeping it for a sufficient time in diluted muriatic or other acid, by which means the earthy part is removed from the bone, which thus becomes soA and flexible; if still retains in a perfect manner its form and volume, although the weight is diminished in proportion to the matter it has lost. The animal substance obtained by this process, has the character of cartilage, and is capable of being reduced by continued maceration into common cellular tissue.
There is another method of displaying the internal structure of bone; viz. by calcination, which destroys the animal matter, and leaves an earthy substance, having the size, form, and a great part of the weight, of the original organ. When a bone is minutely examined in its natural state, or after either of these modes of preparation, it appears to be composed of a great number of fibres, which are variously disposed, and in many places there is an appearance of a laminated structure.
These fibres by their irregular crossing, produce numerous cells, whose size and distinctness vary in the compact and spongy textures. The existence of the laminated structure has been denied by Bichat, who thinks that anatomists have been deceived by the manner in which they prepared the bone for examination. A similar opinion is also entertained by Howship and Scarpa; they contend that the ultimate texture of bone is reticulated; and that the phosphate of lime is deposited in the interstices which are thus formed.
Dr. Bostock, whose sentiments always demand attention in consequence of the cautious manner in which he draws his conclusions, admits the existence of plates in the adult bone. I am myself, however, inclined to agree with the former high authorities; because, if the animal substance which forms the mould of the internal parts of the bone be circfidly examined after a prolonged maceration, no real lamina can be satisfactorily detected.
The osseous matter exhibits other and more striking diversities in its appearance, which are displayed by making sections of bones belonging to different classes, and of different portions of the same bone. These varieties, which principally depend on the inequality of density observed in the interior, have been reduced to two, which are described by anatomists as the compact and the spongy substances.
The former is distinguished by its solidity, which is so great that no interstices can be perceived in it by the naked eye; there are, however, minute canals, which are visible with the microscope. The passages, which were noticed by the older writers, have been examined by Mr. Howship from whose careful observations we learn that their size is variable, being larger towards the medullary cavity than toward the exterior, where they become uniformly smaller; their mean meter is about one part of an inch.
They have no lateral communications with the medullary cavity, but with the external surface; they appear to be lined with a delicate membrane, which conveys the blood vessels destined to secrete the medullary matter which the canals are filled; this matter turns out to be spermaceti, and is of an opaque and white colour.
The spongy substance exhibits varieties in its appearance, which are so considerable that many authors have described them as distinct textures, under names of the reticulatcd, alveolar, cellularated, &c.; are, however, merely modifications of one another. This consists of numerous fibres crossing each other in different directions, and thus intercepting spaces between them of various forms and sizes; in the radius of the cylindrical bone they are large but few in number, whilst at its extremities they are numerous small.
Notwithstanding the apparent distinctness of the compact and spongy textures, they are in reality but one and the same substance, which presents different appearances according to the quantity of the phosphate of lime that it contains. These two structures are met with in various proportions in every bone of the body, the compact forming the external or solid part, and the spongy the internal portion.
The body of the cylindrical bone is formed principally of the compact substance, which decreases in its density towards the interior, and at length ends in an expanded tissue, which being formed of large cells, frequently distinguished by the name of cancellated tissue, or lattice-work; in the centre, the osseous fibres nearly or entirely terminate, so that a hollow may be acco in the cancellated bone, which is occupied in the living object by numerous cells formed by the medullary membrane.
The ends of the long bones are greatly enlarged, and are composed principally of the spongy substance which is covered by a thin crust of the compact texture. The peculiar disposition of the osseous matter in these bones, is admirably adapted to the purposes for which they are destined; the middle is the part most exposed to external violence; now, in order to afford the necessary resistance, the compact substance is accumulated in considerable quantity, and as it is arranged around a centre which is nearly hollow, the circumference of the bone is augmented without any addition being made to its weight.
The advantage of this arrangement is evident; for it is a law of mechanics, that the resistance of a cylindrical body to a force applied transversely, is increased in proportion to its diameter; do that the same number of fibres placed, as it were, round the circumference of a circle, produce a stronger bone than if they had been all united, in the centre, and the diameter of it had been proportionally diminished.
The extremities of the long bones are also excellently contrived, for in them the osseous matter is expanded so to enlarge their diameter, by which means a greater space is afforded for the attachment of the numerous tendons, at the same time that the joints are rendered strong and secure.
In the short bones, the spongy substance is accumulated; and for this reason the os calcis, and others of the same class, possess a porous character; they are covered on the exterior by a crust of denser substance. The compact substance of the broad bones is of considerable thickness; it forms two layers, of which the internal one in the cranium being denser than the outer one, is distinguished by the name of tafaia vitrea.
The spongy tissue, which is similar to that of the ends of the long bone, is often almost entirely deficient towards the centre, where the bones are semi-transparent; in the head, it is called the diplaea. Section V. Organization of Bone. The bones differ so entirely in their appearance and durability from all the other organs of the animal frame that it is difficult to conceive of their structure being essentially the same as that of the soft parts. The principal peculiarity in their composition is owing to the large quantity of calcareous earth which they contain; this substance enables them to resist for a lengthened period the influence of chemical agents, so that they remain for ages the memorials of the dead, the evidence of a former race of men, or of animals which have ceased to exist since the last great revolution of our globe; the proofs of such changes in nature, an we can not trace but by these uncertain marks.
Minute anatomy reveals the complicated organization of the bones; shews their membranes, their blood-vessels, and even their nerves; and thus explains how these organs may be affected with the same diseases as the soft parts, and how, like them, they may, by their own unaided powers, be restored to health. In consequence of the great vascularity of the osseous system, the arteries in the large bones are easily injected, and after the earthy matter has been removed by the action of diluted acid, they may be traced into the internal substance.
There are in general two distinct orders of sanguiferous vessels; one set being furnished by the periosteum, and the other by the artery which passes through the medullary canal. The arteries of the first set, which are very small and numerous, penetrate by the openings placed on the external surface of all the bones; <Callout type="tip" title="Tip">they arc regarded by some anatomists as the only proper nutritious vessels of the osseous texture.</Callout> The arteries of the second class pass through the medullary foramina and canals, and on reaching the interior, each of them divides into two branches, which in the long bones immediately diverge, and then run in a parallel direction with the shaft; they are distributed in an especial manner to the medullary membrane, where they ramify and secrete the marrow; and eventually, having passed through the cancellated texture into the compact substance, they communicate with the arteries of the periosteum. This anastomosis is free in proportion to the youth of the individual; a circumstance which explains the ready union of the periosteum when it has been detached in a young person; and also how it happens that in those cases where the periosteum does not adhere, the bone, provided it has not itself been injured, does not die, but throws up anulations from its surface.
The medullary arteries are accompanied by veins which exactly correspond with them in size and number; but the arteries derived from the periosteum are of a different nature. The blood-vessels of the bones are intimately connected with those of the surrounding parts, and their nutrition is dependent on the general circulation. In cases where the periosteum has been injured or removed, the bone may be nourished by means of the vessels which communicate with the adjacent soft parts; but in such cases, if the injury is extensive, the bone will become necrotic, and ultimately die away.
The bones are strongly marked in the male skeleton, the various processes being large and developed, and the cavities distinct and well defined; this strength of the male corresponds with the fulness and power of the muscular system, with which they are so inseparably connected. The skeleton of the female, on the contrary, is more delicately framed; the bones are small and lightly made; the processes are but little prominent, so that there is an absence of that asperity and inequality which arc so strongly characteristic of the skeleton of the male.
There are also differences which relate to the important function of generation. Thus the clavicle is short, the lumbar portion of the spine is elongated, and the pelvis especially, is very capacious; all these modifications in the dimensions of the trunk, are evidently intended to increase the size of those cavities which receive the impregnated womb.
Section V. Organization of Bone. The bones differ so entirely in their appearance and durability from all the other organs of the animal frame that it is difficult to conceive of their structure being essentially the same as that of the soft parts. The principal peculiarity in their composition is owing to the large quantity of calcareous earth which they contain; this substance enables them to resist for a lengthened period the influence of chemical agents, so that they remain for ages the memorials of the dead, the evidence of a former race of men, or of animals which have ceased to exist since the last great revolution of our globe; the proofs of such changes in nature, an we can not trace but by these uncertain marks.
Minute anatomy reveals the complicated organization of the bones; shews their membranes, their blood-vessels, and even their nerves; and thus explains how these organs may be affected with the same diseases as the soft parts, and how, like them, they may, by their own unaided powers, be restored to health. In consequence of the great vascularity of the osseous system, the arteries in the large bones are easily injected, and after the earthy matter has been removed by the action of diluted acid, they may be traced into the internal substance.
There are in general two distinct orders of sanguiferous vessels; one set being furnished by the periosteum, and the other by the artery which passes through the medullary canal. The arteries of the first set, which are very small and numerous, penetrate by the openings placed on the external surface of all the bones; <Callout type="tip" title="Tip">they arc regarded by some anatomists as the only proper nutritious vessels of the osseous texture.</Callout> The arteries of the second class pass through the medullary foramina and canals, and on reaching the interior, each of them divides into two branches, which in the long bones immediately diverge, and then run in a parallel direction with the shaft; they are distributed in an especial manner to the medullary membrane, where they ramify and secrete the marrow; and eventually, having passed through the cancellated texture into the compact substance, they communicate with the arteries of the periosteum. This anastomosis is free in proportion to the youth of the individual; a circumstance which explains the ready union of the periosteum when it has been detached in a young person; and also how it happens that in those cases where the periosteum does not adhere, the bone, provided it has not itself been injured, does not die, but throws up anulations from its surface.
The medullary arteries are accompanied by veins which exactly correspond with them in size and number; but the arteries derived from the periosteum are of a different nature. The blood-vessels of the bones are intimately connected with those of the surrounding parts, and their nutrition is dependent on the general circulation. In cases where the periosteum has been injured or removed, the bone may be nourished by means of the vessels which communicate with the adjacent soft parts; but in such cases, if the injury is extensive, the bone will become necrotic, and ultimately die away.
Key Takeaways
- Bones are composed of both compact and spongy tissues, each with distinct properties
- The periosteum plays a crucial role in bone nutrition and healing
- Understanding bone structure can aid in triage and treatment decisions
Practical Tips
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