ries and their divisions are strangely contorted and expanded into pouches and dilatations. Erectile formations must acknowledge some other cause more deeply affecting the original formative process, but we do not think with Rokitansky that their cells originate as excavations in a solid blastema. The rapidity with which, when imperfectly removed, they often return again, also indicates a special modification of the laws which determine the formation of tissue.

Enchondroma.-This name was applied by Müller to certain tumors

essentially consisting of cartilaginous structure, whose real nature was first discovered by him. They must be carefully distinguished from all

Fig. 57. Thin section of the circumference of an enchondroma from the pelvis.

Fig. 58. Corpuscles from the softened part of the same tumor.

Fig. 59. The same, after the addition of acetic acid.-Bennett.

those dense white fibrous thickenings which present very much the external aspect of a layer of cartilage. Enchondroma forms usually a

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globular tumor, with a smooth or somewhat tuberiform surface. Internally, a section displays a number of loculi of very irregular roundish shape, filled with a firmly gelatinous, or rather pellucid substance. walls of the loculi consist of a whitish fibrous tissue, more or less closely resembling that of fibro-cartilage; in some much rarer cases, this is replaced by an amorphous, firm, intercellular substance, very similar to that of true cartilage. The gelatinous matter consists of roundish or elliptic cells, varying from th-th inch in diameter, containing granular nuclei, or secondary nucleated cells in their interior. Enchondroma, by boiling, generally yield chondrin, the same substance as is obtained from ordinary unossified cartilage; occasionally, however, it yields glutin. Tumors of this kind sometimes originate in the interior of the bones, which they expand so as to form a thin capsule covering their surface; this is sometimes absent entirely, or may be deficient at certain spots. In the interior of the mass there often remain inclosed portions of the cancellous tissue of the bone. Vogel states that enchondromata may originate also on the surface of bones, especially the flat; in this case they are of course invested only by periosteum, and not by any bony capsule. Enchondroma is occasionally observed in soft parts; it contains then no bone, and its structure is more purely that of hyaline cartilage. The chosen seat of enchondroma is in the bones, especially in the phalanges of the toes and fingers; out of thirty-six cases the metocarpus and phalanges were affected twenty-six times, the tibia three, the ilium one, the cranium one, the ribs one. In the four other cases, the testicle was in two the seat of the disease, the parotid in one, the mamma of a dog in one. Rokitansky mentions having seen it also in the subcutaneous cellular tissue, and in the bony. It occurs most often in the young, but sometimes has not appeared until an advanced period of life; when this is the case it is often associated with exostoses and osteophytes. Enchondroma is of slow growth, and does not usually attain a large size; one instance, however, is recorded, in which the tumor weighed nine pounds and a half. They do not contaminate the system, and only become dangerous if they inflame and ulcerate, and pour out a copious discharge. Cartilaginous tumors are prone to ossify, and in this instance the term is not misapplied, as true bony structure is really found. The ossific change sometimes seems to have commenced at the root of the tumor, at its bony attachment, and to extend outwards towards the circumference, following the progress of the cartilage formation, just as it does during the growth of the shaft of a long bone. In this way a cartilaginous tumor is converted into an exostosis. In other cases ossification commences from numerous independent centres, from which bony fibres radiate in all directions, and would, after a time, become confluent.

MYELOID TUMORS.

In his eighth lecture, Mr. Paget has described, with his usual ability, a class of tumors with which pathologists have but recently become acquainted. They are termed myeloid, from their being usually deve

ries and their divisions are strangely contorted and expanded into pouches and dilatations. Erectile formations must acknowledge some other cause more deeply affecting the original formative process, but we do not think with Rokitansky that their cells originate as excavations in a solid blastema. The rapidity with which, when imperfectly removed, they often return again, also indicates a special modification of the laws which determine the formation of tissue.

Enchondroma.-This name was applied by Müller to certain tumors

essentially consisting of cartilaginous structure, whose real nature was first discovered by him. They must be carefully distinguished from all

Fig. 57. Thin section of the circumference of an enchondroma from the pelvis.

Fig. 58. Corpuscles from the softened part of the same tumor.

Fig. 59. The same, after the addition of acetic acid.-Bennett.

those dense white fibrous thickenings which present very much the external aspect of a layer of cartilage. Enchondroma forms usually a

terior vertebral ligament occasionally ossifies, so do the tendons, fasciæ, and aponeuroses in various parts. Dr. Walshe enumerates the following instances of the formation of bone in areolar tissue, in the submucous tissue of the gall-bladder, in the sub-serous of the pleura, the sub-retinal, the intramuscular, the parenchymatous of the liver. He mentions also ossification of muscular fibre and of the crystalline lens as having occurred.

An exostosis is an osseous tumor, proceeding from the bone or its periosteum, and, according to Rokitansky, homologous in texture, when fully developed, with that of its base and point of origin, whether that be compact or spongy. Its form varies-being sometimes broad and flat, sometimes round and prominent, with a narrow neck, some

times spinous. They do not often attain a size above that of a hen's egg. Sometimes they are single; but often several exist together in the same individual, and even on the same bone. In texture, they vary considerably from that extreme degree of density which constitutes the "ivory exostosis" to the porosity of ordinary cancellous tissue. The compact exostosis "is compact from the very first, and grows in such a way that the layers which are added to it always at once become

as dense as ivory." "When they are minutely examined, the number of peripheral lamina is found to be very considerable, and the corpuscles lying amongst them are long. The Haversian canals are small and far apart," and the corpuscles in some parts are quite absent, in others are closely crowded together. "The spongy exostosis proceeds from a circumscribed rarefaction or expansion of the bony tissue. It forms a tumor of cellular texture, abounding with marrow, which is surrounded by a compact layer or rind." It may originate from the compact outer layer of the bone, or from its spongy interior. In some cases a tumor of this kind contains in its interior a well-formed medullary cavity, communicating with that of the bone. The spongy exostosis may remain in the same condition, or become indurated and more similar to the compact, by the deposition of more earthy substance. If, as occasionally happens, a bony tumor grows inward into the medullary canal of a bone, it is termed an Enostosis. Exostoses often arise without any obvious cause; sometimes they appear to develop in consequence of a blow or strain. "In most cases the periosteum covering them is in its natural condition;" sometimes it is thickened and unusually adherent. They are not peculiar to any period of life; those of the spongy kind have been observed even in new-born infants. Spongy exostoses are sometimes destroyed by caries; and in a few cases the ivory exostosis has become necrosed, and been thrown off. This change must proceed, no doubt, from obliteration of the Haversian canals, and consequent cessation of its nutrition, and would be similar to the shedding of the antlers of the stag.

Osteophytes. To this class belong a great variety of bony growths, which form, for the most part, in inflammatory exudation, are pretty widely spread, in many cases, over a bone, and are rather easily separable from it. In these respects, and in their greater irregularity, they differ from exostoses, which are to be regarded as outgrowths from a bone, while osteophytes seem only to be produced under the influence of a bone. Osteophytes, of warty or stalactitic shape, are very common in the neighborhood of diseased joints, where the articular surfaces are affected with caries. They result, doubtless, from ossification of the exudation, derived from the adjacent hyperæmic vessels. In front of the vertebral joints and some other synchondroses, pretty long styloid or lamellar osteophytes frequently are produced, so as even sometimes to form a kind of bony capsule around them. "They arise from a chronic inflammation of the bones," and while these are atrophied, are often of dense hard texture. Sometimes the osteophyte is said to be foliaceous, consisting of beautiful delicate lamellæ, arranged parallel to each other, and running transversely vertical to the axis of the bone. The flat osteophyte is sometimes an extremely thin and delicate layer (like hoar frost); sometimes it is one or two lines in thickness. It is composed of delicate fibrils and lamellæ, and at first has scarce any attachment to the bone upon which it lies. "At a later period the osteophyte is found attached to the bone by some intervening minute round pillars and plates. After having become gradually compact, it unites with the bone." this variety belongs the puerperal osteophyte, to which attention has of late been particularly directed. An account of this will be given in the chapter on the osseous system.

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