They may be unilocular, usually filled with a solid mass of a fibro-cellular or fibro-cartilaginous character; or multilocular, with thin and serous, sero-sanguinolent, viscid or dark-colored contents, often associated with central, fibrous growths. _Hydatid cysts_ have been met with. According to Stanley, both the acephalocyst and the cysticercus cellulosæ have been found, but more frequently the former. =Tubercles= are occasionally present in bone, as the yellow, opaque tubercles, deposited chiefly in the spongy bones and the cancellous portions of long bones. They may soften or become cretified. =Vascular Tumors= are of not very frequent occurrence. They are met with most commonly in the cancellous articular ends of the long bones; although they have also been found in the pelvic bones, the bones of the skull, and in the ribs. In the most frequent class of cases, a new tissue is developed in the osseous structure, and the tumor partakes of an encephaloid character. A creamy, curdy or brain-like, soft, and very vascular mass, is formed as the essential constituent. This will be found to present every shade of transition, from a purely vascular tissue, of an erectile character, to true encephaloid cancer. In a second, more rare form of disease, there is developed in the bone a _vascular_, _erectile_ growth, closely resembling capillary nævus in its structure, composed of an infinity of blood-vessels, interlacing in every possible way, so as to form a soft, reddish-yellow tumor. In a third form, a hollow cavity is formed in the bone, scooped out of the cancellous structure and filled with blood, partly liquid and partly coagulated, and having arterial branches freely opening into it. According to the stage of the disease, the blood is found in cells, intersected by fibres, or laminæ and fibres, the remains of the original osseous structure; or in a more advanced stage, in a single cavity. The shell of bone surrounding the cavity is very thin and expanded, being usually absorbed at one point, where it often becomes at last perforated. This last class constitutes _true aneurism_ of bone. _Cephalohæmatoma_, met with in infancy on the cranial bones, as a result of pressure during parturition, is an effusion of blood between the pericranium and the bone, commonly occurring on one of the parietal bones, most frequently on the right side. Rare cases of internal cephalohæmatoma have been recorded in which the effusion took place between the dura mater and the bones. =Cancer= of bone most frequently occurs in the head of the tibia and the lower end of the thigh bone, occasionally in the humerus and in the jaws, more especially about the antrum. The encephaloid variety is the most frequent. It is of two distinct forms: in the one, the morbid growth is central, springing from the medullary canal; in the other, it is peripheral, being attached to the compact osseous substance.