years later, when the case came under the care of the writer, there was found in the scar and involving the entire gland a sarcoma larger than a hen's egg. This case and many similar cases must impress the surgeon with the importance of a careful and complete removal of all cartilaginous tumors when a radical operation is deemed advisable.

Testicle. In rare cases the testicle is the seat of pure and of mixed chondromata. Kocher recorded eight cases of pure chondroma. O. Weber saw a case of congenital chondroma of the testicle. The cartilage is usually hyaline, seldom fibrous. The great liability of chondroma of the testicle to undergo malignant transformation is shown by the fact that in half the cases regional and general infection were noted. Paget reports a number of such cases in detail. The tumors are very hard and lobulated, with softer portions between the nodules. Unless the tumor is very small enucleation should give way to castration.

Ovary. Chondroma of the ovary occurs very rarely as an isolated separate tumor. Kiwisch reported two cases of cartilaginous tumors of the ovary, but only in one case was the diagnosis corroborated under

the microscope. Klob has shown. that the cartilage in such tumors appears in the form of large fenestrated plates in the periphery of the tumor, or forms granular prominences, or, finally, is disseminated through the fibrous stroma in groups of cartilagecells the size of a pea.

Connective Tissue.-In exceptional cases chondromata occur in the subcutaneous and deep connective tissue in different parts of the body. Their origin in such unusual localities must be sought in displaced matrices of chondroblasts. The tumors are met with most frequently in situations where such displacements are most liable to occur-that is, in localities in close proximity to parts containing cartilage in the embryo.

FIG. 296.-Accessory auricles of neck (after C. Beck).

Chondroma Branchiogenes.-Chondromata in line with the first branchial tract spring from displaced islands of cartilage derived from the external ear. Some of the cartilaginous tumors in the vicinity of the hyoid bone may derive their matrix from the hyoid bone and larynx,

as suggested by Callender. A number of writers have described accessory auricles in lines of the branchial tracts. Beck of Chicago recently described such a case. Some of these isolated islands of cartilage have become the matrix of cartilaginous tumors the size of a hen's egg and larger. Heusing describes the case of a large cystic chondroma of the neck. In Schäffer's case the tumor was of the size of an egg, beneath the skin on the side of the neck. Beck described a case of accessory auricles of the neck in a man forty-eight years old (Fig. 296).

FIG. 297.-Cartilage from accessory auricles of neck (after C. Beck): a, perichondrium; b, new cartilage-cells under perichondrium; c, reticulum; d, islands of cartilage-cells surrounded by stroma of fibrous tissue.

He removed a particle of one of the cartilaginous masses and subjected sections of it to microscopical examination. The sections showed the typical structure of cartilage (Fig. 297).

In the majority of cases of branchiogenous chondroma the matrix. remains latent until after the age of puberty, as in most of the fourteen cases so far reported the tumors did not develop until some time after puberty.

28

XXI. OSTEOMA.

Definition. An osteoma is a tumor which possesses a structure resembling that of cancellous or compact bone, produced from a congenital or post-natal matrix of osteoblasts. Osteomata occur usually in connection with some part of the skeleton, but they are also found in parts and organs that have no genetic relations with the skeleton, as in the pia mater and the brain. It is doubtful if the tumors which are not in connection with bone present the structure of bone so perfectly as do osseous tumors of the skeleton. Fleischer described an osteoma of the tendon of the ilio-psoas muscle in which he found the Haversian canals and the medullary tissue arranged in the same typical manner as in normal bone. In another heterotopic osteoma described by the same author the tumor was situated upon the inner surface of the dura mater. In both instances bone-production was traced to the connective tissue and independently of the presence of osteoblasts. According to Fleischer's interpretation, the connective tissue at the seat of tumorformation became more vascular and presented active tissue-proliferation, and was transformed into hyaline masses in the interior of which the bone-cells appeared. The hyaline lumps become coalescent and undergo calcification. Osteoblasts were active in the further development of bone. The capacity of connective tissue to produce bone has been recognized for a long time, and this view of the bone-producing power of connective tissue is accepted by most of the modern pathologists.

A distinction must be made between calcification and ossification of connective tissue. The production of bone is carried on in the embryo by a distinct and specific part of the mesoblast, resulting in the formation of the skeleton and the growth of bone, and the production of new bone can take place only from a matrix of cells derived from the osseous system. The displacement of osteogenetic matrices into the surrounding tissues is as liable to occur as the displacement of matrices of epiblastic and hypoblastic tissue. Heterotopic osteomata are usually found in close proximity to a bone. Heterotopic matrices of osteoblasts usually result in imperfect development of the tissue of the tumor. Virchow found in the apex of the lung an osteoma in which Haversian

canals and medullary spaces were absent. Steudener found a number of small osteomata near the trachea, but entirely distinct from its rings. Lesser found in the lung an osteoma which presented under the microscope all the histological elements and the typical structure of bone.

The metaplastic theory concerning the origin of bone is no longer tenable. A careful etiological distinction must also be made between a true osteoma and an exostosis. The origin of the former must be restricted within the limits of the definition to a growth of bone from a matrix of osteoblasts either in the bone or by displacement from a bone, while the latter is the result of a localized or diffuse hypertrophy usually following a reparative process.

Histogenesis. The osteomata representing compact bone are usually found upon the surface of bone, and they appear to be produced from the periosteal osteoblasts, as in the case of bony tumors of the flat bones of the skull and of the shafts of long bones; or they begin as chondromata, and proceed most commonly from the epiphyseal lines and from the places of origin of ecchondroses. The latter group of tumors, which have therefore a mode of origin distinct from the preceding, are usually pedunculated, are covered with cartilage, and possess a cancellous structure continuous with that of the bone from which they arise. Osteomata from a displaced matrix of osteoblasts are found most frequently at the insertion of tendons. Ossification of the deltoid from the shouldering of arms in the soldier, ossification of the adductors of the thighs in cavalrymen, and the more diffuse bone-formation in myositis ossificans do not belong to osteoma, but occur as one form of muscular degeneration.

Histology. In spongy osteoma (Figs. 298, 299) the cancellated structure of the bone is well shown in decalcified stained sections. If the tumor starts in the bone, it is surrounded by a zone of connective tissue which separates it from the surrounding tissues. In the ivorylike tumors upon the surface of the cranial bones and the shaft of the long bones the lamellæ are so compact that the medullary spaces and the blood-vessels cannot be identified. The section of such a tumor resembles ivory in compactness. In periosteal osteoma the tumor is at first not connected with the underlying bone, and at this stage can readily be detached. Later the surface of the tumor becomes attached to the bone and receives from it a part of its vascular supply. After the union has become complete a section through the tumor does not show the line where the union was effected.

In the development of an osteoid chondroma into an osteoma the different phases of transition of cartilage into bone-tissue can be observed. Osteoma is almost immune to the different regressive meta

FIG. 298.-Spongy osteoma of cranium; X 250 (after Perls): a, old bone-tissue with thick cancelli parallel with the surface; b, young spongy bone-tissue with irregularly-arranged cancelli.

FIG. 299.-Osteoma of finger: X 30 (after Karg and Schmorl). The tumor (a), separated by a narrow zone of connective tissue (b) from the epithelium of the surface (c), consists of cancellous tissue. The narrow cancelli with delicate contour include the bone-cells, which appear as minute black dots and are covered on the surface with cells arranged like epithelium. Between the cancelli is a substance like myeloid tissue, which toward the periphery of the growth shows many nuclei.