746 THE BONES AND JOINTS. 



i.e., those growing from the medulla, are rare. They usually occur in 

 the lower jaw, but have been found in the ends of the long bones, the 

 phalanges of the fingers, and the vertebrae. The fibromata may calcify 

 or ossify, contain cysts, and not infrequently occur in combination with 

 sarcoma. 



Myxomata are of occasional occurrence in bone. 



Osteomata. New formations of bone as a result of inflammatory proc- 

 esses are, as we have already seen, of frequent occurrence in bone, and 

 although not, strictly speaking, tumors, some of their forms are very 

 closely allied to them, and they may therefore be conveniently mentioned 

 here. New growths of bone which arise from the surfaces are called 

 exostoses (see Fig. 482) or enostoses, according to their origin from the 

 external surface or from the interior of the bone. They may contain all 

 the constituents of normal bone : bone, medulla, vessels, periosteum, and 

 cartilage. The new bone may be compact and like ivory, or spongy, or 

 contain large cavities filled with marrow. 



The shape of exostoses varies greatly ; they may be in the form of 

 sharp, narrow spicula and processes, and, occurring in connection with 

 periostitis, are called osteophytes. They may be polypoid in shape, or 

 form rounded tumors with a broad base. They may form a general 

 enlargement of the bone with much roughening of the surface ; this con- 

 dition is often called Tiyperostosis. 



The bone beneath these new growths may be normal, or sclerosed, or 

 rarefied, or the medullary cavity of the bone may communicate with that 

 of the exostosis. Exostoses are usually developed from the periosteum, 

 sometimes in the insertion of tendons and ligaments. They are very 

 frequently multiple, and may occur at all ages, even during uterine life. 



Enostoses are developed in the interior of bones from the medulla. 

 They may increase in size, with absorption of the surrounding bone, until 

 they project from the surface like exostoses. Their most frequent situa- 

 tion is in the bones of the cranium and face. 



Chondromata. These tumors may be single or multiple, and most fre- 

 quently grow from the interior of the bone, but sometimes from the 

 periosteum. They are prone to form various combinations with other 

 forms of tumors, as fiboma, myxoma, sarcoma, etc. They are frequently 

 congenital, and are most common in young people. They occur most 

 frequently in the bones of the hand and foot. 



There is a form of chondroma, called osteoid chondroma, which develops 

 beneath the periosteum, most frequently in the femur and tibia near the 

 knee joint, forming a club-shaped enlargement of the bone. The char- 

 acteristic of the tissue composing these tumors is that it resembles some- 

 what the immature bone tissue which is seen beneath the periosteum 

 in developing bone. It differs from cartilage in the irregular shape of 

 its cells, in the~ fibrillation and density of the basement substance, and in 

 its general vascularity. On the other hand, it has not the inorganic con- 

 tents or appearance of true bone. It resembles considerably the callous 

 tissue forming about fractures of the bones. It may, however, and most 



