PATHOLOGY 371 becomes a kind of cartilage. The tumours in question are most common, at least, just at the time of life when that change in the character of the marrow takes place. Again, at the spongy ends of bones, where the marrow remains red, the internal enchondromata rarely occur (a case is quoted by Paget at the lower end of the fibula), but chiefly the subperi osteal. If the enchondromata were composed of a definite type of cartilage, and, above all, if they were stable in their structural characters, the relation of them to the marrow of bones, which these facts point to, would not be a very intelligible one. But the enchondromata are rather a kind of new growth in which there is a good deal of gristly substance of one kind or another, associated with a good deal of mucous or myxomatous tissue, with cystic spaces containing mucous or honey-like fluid, and even with blood-spaces. Besides the myxomatous tissue, there may also be tracts and areas of other soft tissue made up of spindle-cells, multinuclear cells, and various Fio. 30. Foi tal or parenchymatous cartilage from enchondroma of upper jaw (horse). (The hyaline intercellular substance is left out.) FIG. 31. From enchondroma of upper jaw of woman ; a few large cartilage- cells in a tissue consisting mostly of branched cells. nondescript forms ; and, most significant of all, there may be much of the cartilaginous substance quite fcetal in its characters, that is to say, consisting almost entirely of cells, with a small amount of more or less tough hyaline intercellular substance. Fig. 30 shows a highly cellular kind of cartilage from a tumour of the upper jaw of a horse. The next cut (fig. 31) is from a cartila ginous tumour of the upper jaw of a woman ; it shows cartilage- cells with definite capsules, and surrounded by a kind of tissue which would be called myxomatous. The shades of difference among the tissues of enchondromata are indeed endless. They may be said to be all possibilities open to the red marrow (hremato- blasts) on the way to become fat ; sometimes one devious route is taken, sometimes another, and the result may be soft mucous tissue, various forms of cartilage, or true bone as an ulterior development of the cartilage. Osteoma. Next to the enchondromata among the tumours of bone we may take the ostcomata, or outgrowths from the bone which have themselves the structure of true bone. Their most itosis. common form is the exostosis, an osseous node or spine, or rounded tumour generally, on the outer surface of a bone. Some times an exostosis is found covered by a considerable cap of car tilage ; and, whether it be or had been partly cartilaginous, or whether it be entirely osseous, it is a product of the periosteum, and it illustrates the ordinary osteoblastic function of that tissue. Sometimes the exostosis is spongy, at other times it is hard as ivory, the flat bones of the head being the favourite seat of the latter variety. old Osteoid Tumours (Subperiosteal Malignant Tumours). By far the our. most important of the tumours of bone are those which are com posed of a crude kind of bone, or of various kinds of soft tissue which show a more or less ir^^- ^-s**-." i 3go= feeble tendency to osseous transforma tion. These tu mours of the bones are apt to occur during the growing period, or shortly after growth has ceased ; they are by no means rare, and are often fatal 1 . Like the enchondromata, they are divided into those which grow under the perios teum, or the external tumours of bone, and those which begin in the medullary canal, or the internal. The former are much the least complex ; and, like the subperiosteal enchondromata, they are mostly found at the ends of long bones, especially at the end of O FIG. 32. Structure of osteoid tumour. the femur. The growth is clearly subperiosteal ; the outlines of the compact bone of the shaft can often be seen running through it. The structure of this kind of tumour is tolerably uniform ; it is not bone, but an irregular product of the periosteum to which the name of "osteoid" lias been given. The structure is that shown in fig. 32. There is a network of slender trabeculre, mostly form ing long parallel meshes, and with numerous but less conspicuous cross subdivisions; these are impregnated with osseous salts ; but it can hardly be said that bone-corpuscles are embedded in them, as in the normal growth of bone from periosteum (fig. 33). The cells which correspond to the osteo- blasts are ranged along the sides of these trabe- Fl "- 3 i 2 -T Spic i ulc , , fl T <? ssif > in K parietal bone culre and in the spaces < kltten); "steoblasts becoming included as bone-corpuscles, between them ; but they fall short of the true osteoblastic grouping, and they seldom become bone-corpuscles embedded in an osseous ground-substance. This is a peculiar error of the osteoblastic process, but a not unintelligible one. It may be further illustrated by another form of periosteal tumour in which there was no deposition of the hardening matter at all. This tumour (fig. 34) grew around the metatarsal bone of Softperi- the little toe, and, like the osteoid kind of tumour last described, osteal it had a power of infecting the neighbouring tissues and even dis- tumour, tant organs, which need not be dwelt upon at present. The struc ture is a strange reminder of the inherent osteoblastic function of the periosteum from which it grew. There is not a particle ^j^^ * FIG. 34. Periosteal tumour of lifth metatersal bone. of osseous or earthy matter in its substance ; but it has the trabe- cular type of osteoid tissue, and the cells have the surface-grouping of osteoblasts. They are the elongated or spindle-shaped cells of the periosteal tissue, which have become more cubical and angular, and have formed rows of free cells round the walls of the inter stitial slits or alveolar spaces. The difference between this and an osteoid tumour is that a certain attempt has been made in the latter towards true bone in the deposition of earthy or bone salts in the trabeculre. In the case of the soft tumour of the periosteum there were clear traces of rickets in infancy, and the essential thing in rickets is the tardy or inadequate deposition of earthy matter in the growing bone. In both tumours the formative activity of the periosteal cells outruns their osteoblastic and ossifying functional activity, so that the latter is always behind, and the perfect result of hard bone is never attained. How this error makes a malignant tumour is another and more difficult question. Mycloid and other Internal Tumours of Bone. The foregoing are Myeloid representative instances of external or subperiosteal tumours of bone- bone in addition to the enchondromata and osteomata. There tumour. remains an important group of internal tumours, or tumours of the bone-marrow ; and these, with the corresponding group of internal enchondromata, exhaust the morbid new formations incidental to the growth of the skeleton. There is, indeed, no hard-and-fast line between the enchondromata and the internal tumours of bone ; the latter have almost the same mixture and confusion of structure in various parts that the cartilaginous tumours have. The principal seat of the soft tumours of the bone-marrow is the lower end of the thigh-bone, the ends of the other long bones being the next most favourite seats. A certain tumour of the jaws, the mycloid cpulis, is also classed with them. The tumour often grows quickly, and may attain an enormous size ; it causes the absorption or trans formation of the hard walls of the bone, and there may be nothing between it and the skin, muscles, and tendons but a more or less continuous thin shell of bone. The interior has a most diversified aspect. Many patches are friable and yellowish, other areas are a livid purple and gelatinous, and there are often blood -clots and cystic spaces filled with a tenacious brownish mucous or colloid fluid. Amidst these softer parts there run tracts of more spindle- celled or fibrous tissue, and there are often islands of cartilage, or fragments of osteoid substance. The only clue to this puzzling diversity of texture is the inherent range of possibilities in the function of the bone-marrow. Derived from embryonic mesoblast,
