chondromata through transportation of particles in the circulation. Such cartilaginous emboli have often been demonstrated. The secondary growths are most frequent in the lungs. Metastatic chondromata are, however, more frequently chondrosarcomata than pure chondromata.

OSTEOMA.

Definition.-An osteoma is a tumor composed of osseous tissue. Osteomata are closely allied to cartilaginous tumors, and frequently transformations occur.

Etiology. The same difficulty is experienced in distinguishing inflammatory outgrowths or exostoses from true bony tumors, as in the case of cartilaginous growths. Enlargement

of the facial bones in leontiasis ossea, of the bones of the extremities in acromegaly and hypertrophic pulmonary osteo-arthropathy, and ossifications of the muscles in myositis ossificans, are instances of border-line conditions separating true tumors from inflammatory hyperostoses. Irritation and traumatism undoubtedly play a part in the etiology, even in neoplasms unattached to the bone, and in the case of bony outgrowths injury is generally the immediate cause. An underlying predisposition undoubtedly exists, and explains the occurrence of congenital multiple bony

tumors.

Appearance.-Two forms may be distinguished, as in the case of chondromata: (1) outgrowths or exostoses and osteophytes, and (2) the osteomata proper, or heteroplastic osteomata. Exostoses and osteophytes are distinguished one from the other by their shape and appearance rather than by any essential difference. The former are direct outgrowths of more or less wart-like character; the latter are more extensive and present the appearance of bony deposits upon bones, and are less closely attached (Fig. 44). In both forms

the surface of the growth is irregular, nodulated, or wart-like (Fig. 45). The consistency is that of bone, and the size varies

from that of small outgrowths to

masses as large as a fist. On section two forms may be distinguished; the hard or osteoma durum, and the soft or osteoma spongiosum. Sometimes the substance of the tumor is exceedingly dense, and the term osteoma eburneum is applied.

The heteroplastic osteomata, or those separated from the bone, are more rounded and, when of considerable size, usually nodulated and lobulated. In the serous membranes they occur as flat bony plates.

Seats.-Osteomata spring from the bone or cartilage, or from .connective tissue near the bones. More rarely they arise in other connective tissues, in the serous membranes, or in certain organs, notably the testicle and parotid gland.

Osteomata connected with bones are most frequent about the epiphyses, at the attachments of muscles, or at the seat of old fractures from which abundant callous has been deposited. The skull-bones may be affected on the outer or inner surface, and often an elevation is noted without and within at the same spot. A form of clinical importance is that in which exostoses occur on the inner aspect of the metatarsal bone of the great toe from compression of tight shoes. In the maxillary bones osteomata may originate about the roots of malformed teeth. In cases of accumulation of cement-substance beginning at the neck of the tooth the term dental osteoma is applied; these are strictly comparable to osteomata. In cases in which proliferation of the dental pulp has occurred the term odontoma is applicable, and the tumor is not of osseous character. The bony growths sometimes seen in the serous surfaces nearly always arise in areas in which there has been thickening from chronic inflammation. They are most frequent in the dura mater of the brain, particularly the falx cerebri; though the membranes of the cord, the pleura, or pericardium may be involved.

Structure.-Microscopically osteomata resemble more or less accurately bone-tissue. They vary, however, in different areas, and mixtures of cartilage with bony tissue are frequent. Secondary degenerative changes (softening) may occur and association with tumors of other character are not infrequent (chondroma, myxoma, fibroma, sarcoma).

Nature. These growths are eminently benign, do not recur, and do not give metastasis. Their situation sometimes makes them troublesome or dangerous.

LYMPHANGIOMA.

A lymphangioma is a tumor composed of dilated lymph-vessels or lymph-spaces; more frequently the latter. It is difficult to separate dilatations of lymphatic channels due to obstruction from hyperplastic processes. Congenital enlargements of certain parts are met with which seem entirely dependent upon the abnormal development of the lymph-spaces. These constitute the condition. called elephantiasis congenita mollis, in which the subcutaneous tissues are boggy or edematous, and even distinct cystic formations occur. Congenital cystic hygroma is an instance of dilatation of the lymph-spaces. Congenital enlargement of the tongue, termed macroglossia; of the lips, macrocheilia; and of the skin, novus lymphaticus; are other instances of the same process. In all of these, in addition to the dilatation of the lymphatic spaces, a marked proliferation of the connective tissues as well as the muscle (in the case of the tongue) is striking; but the process in all probability originates as a dilatation of the lymph-spaces. The terms lymphangioma cavernosum and cavernoma lymphaticum have been suggested for these cases of dilatation of the lymphspaces. On staining with silver-salts the endothelial lining of the spaces may be readily demonstrated. Actual enlargement and varicosity of existing lymphatic vessels may occur, but is extremely rare in the form of circumscribed growths; it is met with more frequently in association with general processes, such as elephantiasis. The bursting of dilated lymphatics may lead to lymphorrhea or external discharge of lymph when the process involves the skin, or to effusions of lymphatic character when the serous cavities are involved. Chylous pericarditis, pleuritis, and ascites are thus produced. Rupture of dilated lymphatics along the urinary tract (kidney or bladder) occasions chyluria. Lymphangioma is a benign process in the pathologic sense.

HEMANGIOMA.

Definition. An hemangioma, or angioma as it is more frequently called, is a tumor-like formation composed principally of blood-vessels. Strictly speaking, many of these are not tumors, being merely, localized dilatations and elongations of pre-existing blood-vessels. Some, however, represent actual proliferations. Two varieties may be described, that in which the blood-vessels are merely distended (angioma teleangiectaticum), and that in which there are enlarged spaces lined with endothelium (angioma cavernosum or cavernoma). In many tumors the blood-vessels are somewhat enlarged; these are spoken of as teleangiectatic.

Etiology.-Congenital malformation certainly plays some part in certain cases, as the frequency of hemangiomata in the new-born and particularly at the junction of the branchial arches would indicate. Injury, however, and mechanical causes generally also play a part, and pre-existing disease, particularly fibroid inflammatory processes, may contribute to the subsequent dilatation and proliferation of the vessels (see below).

Appearance and Seats.-The angioma teleangiectaticum may involve only the arterioles and capillaries, and in this case a bright-red color is observed. The tumor appears as a spot on the surface of the skin, more or less sharply outlined from the surrounding tissue. It is not elevated and has the same consistency as the healthy parts. Usually it occurs as a multiple condition, and the larger are often surrounded by smaller spots. The skin is the favorite seat; but the subcutaneous tissue and sometimes the mucous membranes are involved. Less commonly the veins are implicated, when a dark-red color is observed (port-winestains).

If a circumscribed portion of the circulation is uniformly involved, the vessels thicken and elongate, and a peculiar form of hemangioma results. In these cases the arteries are greatly thickened and tortuous, and form bunches under the skin, suggesting to palpation a bundle of earth-worms; while the surface of the skin presents peculiar irregular elevations without of necessity any change of color (aneurysma racemosum seu cirsoideum). This is not infrequent in the scalp. A similar condition of the vessels is observed in the varicosity of the legs, labia, or other parts. It is most frequent in the hemorrhoidal veins, constituting the ordinary hemorrhoids. (These conditions will be more fully described in discussing the diseases of the vessels.)

Cavernous angiomata present themselves as more distinctly tumor-like formations of dark venous color, involving the skin or subcutaneous tissues, the retrobulbar tissue of the eye, the mucous membranes of the nose or pharynx, and certain organs, as the mammæ, the kidney, the spleen, but particularly the liver. Like the other variety, they may be congenital, but more frequently arise in later life, especially that of the liver, which is most common in old persons. The appearance is that of a more circumscribed tumor, sometimes showing a distinct capsule and varying in consistency with the degree of distention of the blood-spaces. In the skin it projects slightly from the surface (nævus prominens); in the liver the tumor does not project.

Structure. The definition explains the structure in general. The blood-vessels of teleangiectatic angiomata may be simply dilated capillaries with a lining of endothelium and a fibrous outer coating. More commonly the vessels are considerably thickened and held together by a reticular connective tissue. In rare in

stances the vessels are so closely packed and the walls so thickened that when the blood is removed the appearance is not unlike that of the tubules of a sweat-gland. The cavernous angiomata present large spaces lined with endothelial cells (Fig. 46). Between these

spaces are parallel fibers of connective tissue which form the framework of the tumor. In cases involving the liver the proper substance of this organ disappears completely, leaving only anastomosing spaces with a fibrous framework. Virchow taught that the fibrous process was primary, and by traction and pressure gradually induced dilatation of the vessels and atrophy of the liver-substance. Some of the more recent writers believe that the dilatation of the vessels is the primary condition. The capsule sometimes found surrounding the cavernous angioma is certainly a secondary formation.

Angiomata of the skin may enclose the hair-follicles and sweat-glands; those of the subcutaneous tissue frequently show areas rich in fatty tissue (angiolipoma); secondary angiomatous change of tumors is probably the result of dilatation of the preexisting or new-formed vessels. Sometimes secondary change may occur in the connective tissue of the vessels of an angioma, as in the plexiform angiosarcomata, in which the blood-vessels are surrounded by ensheathing sarcoma-cells (see Fig. 46). Certain cylindromata have the same origin.