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PERIOSTEAL OSSIFICATION.

429

low power, it is at once perceived that the disposition of the constituent parts is entirely that of a bone, for (primary1) medullary spaces and trabecular networks alternate with each other, just as if the observer had before him the medullary spaces and trabeculæ of a spongy bone. The substance which forms the trabecular networks, is on the whole dense, and is therefore readily distinguishable, even with a low power, from the more delicate substance which is enclosed by the trabeculæ and fills the cavities of the meshes. This latter substance presents, when more highly magnified, a finely striated, fibrous appearance. The bands of fibres in part run parallel to the borders of the trabeculæ. In these latter the same structures can be seen with a high power, that are usually presented by bone, namely jagged corpuscles, distributed with great regularity.

This structure exactly corresponds to that which we have seen in the development of bone from periosteum; it is, in short, the plan followed in the growth of bone in thickness. Wherever young periosteal deposits are examined, there is found in the meshes of the network, formed by the osteoid substance, this primary marrow containing fibres, but no cells, as is the case at a later period. This primary marrow consists of the remains of the periosteum itself (after its proliferation), which have not yet undergone the transformation. The transformation into osteoid tissue advances into the proliferating periosteum in the first instance always in such a way, that the fibrous tissue becomes condensed (sclerotic), though only partially so, the condensation be

The primary medullary spaces formed out of periosteum are subsequently all filled with compact bone, and it is by the conversion of this into true, mucous medullary tissue, abounding in cells (which afterwards take up fat) that the secondary medullary spaces are formed. Of the primary medullary spaces formed out of cartilage, however, a considerable number do not pass through any such intermediate stage as that just described as occurring in periosteal ossification, but become at once filled with true medullary tissue and are therefore equivalent to the ordinary, secondary medullary spaces.-From a MS. note by the Author.

ginning at the bone and proceeding outwards in certain directions; in this way there arise, at first resting like columns upon the bone, hardish cones' which are united by transverse bands, parallel to the surface of the bone, and

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thus constitute this network. If now acetic acid be applied to these parts, we see at once that the whole fibrous mass which fills the alveoli, contains the most wonderful connective-tissue-corpuscles, which are so arranged, that next to the trabeculæ all round they lie in concentric rows, whilst in the most internal parts of the marrow they constitute stellate corpuscles which anastomose with one another, as you have already seen on many occasions. But that in some parts the trabeculæ have already become true bone, one may very beautifully convince oneself at the spots, where calcareous salts are really deposited in them. Whilst the periphery of such calcified trabecula (Fig. 131) offers a

Fig. 132. A portion of Fig. 131, more highly magnified. o, o. The osteoid trabecula; m, m, m the primary medullary spaces with spindle-shaped and reticulating cells. 300 diameters.

1 These are the little columns mentioned in p. 81 as being perpendicular to the long axis of the bone, and as intervening between the Haversian systems.

Transl.

FORMATION OF BONE FROM CONNECTIVE TISSUE. 431

brilliant, almost cartilaginous appearance, in their middle an opaque, finely granular matter presents itself which pervades the intercellular substance, and towards the interior of the trabeculæ passes into a nearly homogeneous, calcareous layer, in which at intervals the osseous corpuscles may be recognized. Here we have therefore already a complete osseous network, and at the same time an exact picture of the regular growth of bone in thickness.

If, however, the spots are very carefully examined, where the borders of these trabeculæ and bands of bone come into contact with the fibrous substance of the meshes, it is seen that no perfectly defined limit exists there, but that the intercellular substance of the osteoid tissue is gradually lost in the intercellular substance of the fibrous marrow, so that here and there a few of the connective-tissuecorpuscles of the fibrous connective tissue are included in the sclerotic substance of the trabecula. Hence you may infer, that the formation of real osseous substance from connective tissue is essentially effected by the gradual change of the intercellular substance, and that this loses its originally fibrous nature and becomes converted into a dense, shining, cartilaginous mass, without its ever really attaining however to the structure of cartilage. Here there is never a stage exactly corresponding to any of the known forms of cartilage, but it is out of connective tissue that we see the osteoid substance directly arise, which in cartilage also and marrow is the first to arise when they become bone. This is so far very important, that you can from all these instances acquire the conviction that people have been mistaken in speaking of the cartilage of bone (Knochenknorpel). Cartilage as such can only calcify; when it is to become bone, a transformation of its tissue must take place, the chondrine-containing basissubstance must become converted into a gelatine-yielding intercellular substance.

I have moreover, gentlemen, made a series of preparations from ricketty bones for you-on the one hand, because rickets above all offers an especially favourable opportunity for obtaining an insight into several processes of the normal growth of bone, which in other cases are obscured by the presence of calcareous salts-and on the other hand, because you will thus form some idea of the peculiarity of this process, as such.

Rhachitis, has, as you are aware, by more accurate investigation been shewn to consist not in a process of softening in the old bone, as it had previously generally been considered to be, but in the non-solidification of the fresh layers as they form; the old layers being consumed by the normally progressive formation of medullary cavities, and the new ones remaining soft, the bone becomes brittle. But besides this essential feature of the non-occurrence of calcification in the parts, there is displayed also a certain irregularity in growth, so that stages in the development of bone which, when the formation is normal, ought to set in late, set in at a very early period. In normal growth, the pointed processes, in which shape the calcareous salts shoot up into the cartilage, form, along the margin of calcification, such a completely straight line, that it should almost be described as mathematically regular. This condition ceases to obtain in rickets, and the more so, the greater the severity of the case; interruptions occur in such a way, that in some places the cartilage still reaches a long way down, whilst in others the calcification has mounted up to a considerable height. These uncalcified parts sometimes become so completely separated from one another, that they remain forming specks of cartilage in the midst of the bone, and surrounded on all sides by it-and that cartilage is still found at points where the bone ought long since to have become transformed into medullary tissue. The farther the pro

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cess advances, the more, however, do we also meet with isolated, scattered masses of lime in the cartilage, in many instances to such a degree, that the whole of the cartilage on section appears dotted with white points. The irregularity of the process is further shown in this, that, whilst in the normal course of things the medullary spaces should begin to form only at a short distance behind the margin of calcification (Fig. 126), they here exceed these limits, and in many cases a series of connected cavities extends far beyond the border of calcification, which are filled with a soft, slightly fibrous tissue, and besides have vessels running up into them. Medullary spaces and vessels are therefore met with, where normally and properly not a single medullary cell, and scarcely a single vessel ought to be found.

In this manner there may at all times be found side by side in the parts, where the process has attained its height, a whole series of different histological conditions. Whilst in other cases we find at a certain definite point cartilage, at another calcification, at a third, bone, or medullary tissue, here everything lies in the greatest confusion; in one place, medullary tissue, above it osteoid tissue or bone, by its side calcified cartilage, and below it, perhaps, cartilage still retaining its original condition. The whole of the rhachitic portion of the diaphysal cartilage-and it may extend for a considerable distance-of course acquires no real firmness, and this is one of the chief causes of the liability to distortion, which ricketty bones exhibit, not in the continuity of the diaphyses, but at the articular ends. This is in many cases extremely considerable and is the sole cause of many a deformity, as, for example, in the thorax. The curvatures in the continuity of the bones are always infractions,' those of the epiphyses are

1

By infraction I understand an incomplete fracture (solution of continuity) within the periosteum which remains intact.-From a MS. note by the Author.

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