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convey to it. The vessels which spring from the nutrient artery mark in all bones, at a tolerably early period, pretty exactly the limits to which the ossification subsequently proceeds, whilst the remnants of the cartilage which remain bordering upon the joint never contain vessels.

With regard to the bones themselves, the disposition of their blood-vessels is in itself tolerably simple, but at the

Fig. 32.

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same time very characteristic. If we examine the compact substance, we can usually, even with the naked eye, distinguish upon its surface small openings through which vessels enter from the periosteum. With a moderately high power we discover that these vessels (Fig. 32, a) immediately beneath the surface form a network with somewhat long meshes, or a series of tubes anastomosing with one another

Fig. 32. Longitudinal section from the cortex of a sclerotic tibia, a, a. Medullary (vascular [Haversian]) canals, between them the bone-corpuscles for the most part parallel; but at 6 (in transverse section) concentrically arranged. 80 diameters.

and, generally speaking, running longitudinally, for though they sometimes take a somewhat more oblique course inwardly, they still essentially maintain a longitudinal direction. Between.these meshes there remain comparatively wide interspaces, within which, precisely as we before saw the cartilage cells, we here see the bone-corpuscles, and indeed also in a longitudinal direction, parallel to the surface. If the same part be examined in transverse section, we of course see, where the longitudinal canals were previously observed, nothing but their transverse sections here and there united by oblique communications. Between them lies the proper osseous tissue, deposited in lamellar layers, some of them parallel to the surface, some concentrically arranged around the vessels. In the deeper layers of the compact substance this concentric arrangement around the vessels constantly prevails.

Fig. 33.

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Between these more lamellated parts is left a small quantity of osseous substance (Fig. 33, i) which does not

Fig. 33. Section of bone. a. Transverse section of medullary (vascular [Haversian]) canal, around which the concentric lamellee, I, lie with bone-corpuscles and anastomosing canaliculi. r. Lamella: divided longitudinally and parallel, i. Irregular arrangement in the oldest layers of bone. v. Vascular canal. 280 diameters

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present the same structure, but is arranged upon another, and independent, plan. Upon more accurate examination it is seen to be formed of little columns, which for the most part are perpendicular to the long axis of the bone, and are disposed in a sort of arch parallel to the long axis. These are the remains of the spicula first formed during the growth of the bone in thickness and are therefore of older date.

As in the sections which are obtained by grinding down bone, the vessels themselves cannot for the most part any longer be distinguished, the cavities [Haversian canals] (Figs. 32, a, 33, a, v,) in which they run have been named medullary canals, improperly, inasmuch as there is usually no marrow contained in these narrow channels; they should properly be called vascular canals; still the other term is so

Fig. 34.

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universally received, that it is even employed in cases where the wall of the vessel is in immediate contact with the

Fig. 34. Bone. corpuscles from a morbid formation of bone in the dura mater of the brain. Their branching and anastomosing prolongations (canaliculi) are seen, as well as minute spots upon their walls, marking the funnel-shaped commencements of the canaliculi. 600 diameters.

internal surface of the cavity. Immediately surrounding these canals we see a series of peculiar structures; oblong or roundish bodies which usually appear black when the object is not fully brought into focus, and are provided with jaggs or processes. They used to be called bone-corpuscles, and their processes bone-canals (canaliculi ossei); and as the view was originally entertained that the calcareous matter was really deposited in them, and that the dark appearance which they usually present when viewed by transmitted light resulted from the presence of this matter, the canals were also termed canaliculi chalicophori, a name which has now been altogether abandoned, because convincing proofs have been obtained that, so far from being contained in them, the lime is, on the contrary, diffused throughout the homogeneous basis-substance which lies between them.

As soon as this discovery was made, that, namely, the distribution of the lime in the osseous tissue took place in a manner just the reverse of that in which it had been supposed it did, the other extreme was immediately run into, and for the name of bone-corpuscles that of bone-cavities (lacuna?) was substituted, and it was assumed that bone contained nothing but a series of empty cavities and canals, which were indeed penetrated by a fluid, but still were really nothing more than fissures in the bone. Some few observers indeed actually called them bone-fissures. Now I have endeavoured to demonstrate in various manners that they are real corpuscles, and not mere cavities in a dense basis-tissue, but structures provided with special walls and boundaries of their own, which separate them from the intermediate substance. For by the help of chemical reagents (concentrated mineral acids, and particularly hydrochloric acid) we are enabled, by dissolving the basissubstance, namely, to disengage the corpuscles from it. In this way we furnish, I think, the most complete demonstration that they are really independent structures. Besides,

DEPENDENCE OF TISSUES UPON TIIE VESSELS. 83

a nucleus may be distinguished within these bodies; and, even without entering into the history of their development, we discover that here too we have once more to deal with cellular elements of a stellate form. Bone therefore exhibits in its composition a tissue, containing, in an apparently altogether homogeneous basis-substance, peculiar, stellate bone-cells distributed in a very regular manner.

The intervals which exist between every two of the vessels in bone are often very considerable; whole systems of lamellae, beset with numerous bone-corpuscles, thrust themselves in between the medullary canals. Here it is certainly difficult to conceive the nutrition of so complicated an apparatus to depend upon the action of vessels some of them so remote, and especially so, to understand how every individual particle of this extensive compound mass can manage to maintain a special relation of nutrition to the vessels. For experience shows us that every single bone-corpuscle really possesses conditions of nutrition peculiar to itself.

I have laid these details before you, in order to point out to you the gradual transition which takes place from the vascular and abundantly vascular, to the scantily vascular and non-vascular parts. If we would form a simple conception of the conditions of nutrition, I think we must lay it down as a logical principle, that whatever is enunciated with regard to the nutrition of very vascular parts, must also hold good for that of scantily and nonvascular parts; and that, if the nutrition of individual parts is considered to be directly dependent upon the vessels or the blood, it must at all events be demonstrated that all the elements which stand in immediate connection with one and the same vessel, and are assigned to a single vessel for their support, present conditions of life essentially similar. In the case of bone, it would be necessary to show that every system of lamellae which has only one vessel for its nutrition, always exhibits a similar state of nutrition. For if that vessel, or the blood which ciiculatcs

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