748 



THE BONES AND JOINTS. 



bone tissue, called osteoid tissue, which may in part become calcined, the 

 calcification usually occurring in the central portions, leaving a softer 

 peripheral zone. This form of tumor is most apt to occur at the ends of 

 the long bones, and may form tumors of large size. It is often called, 

 on account of its tendency to extend and to form metastases, malignant 

 osteoma or osteoid cancer. Angio- sarcomata 

 are of frequent occurrence in bone. 



Sarcomata may originate in the medulla 

 myelogenic 1 and may grow rapidly. 

 The bone surrounding them is destroyed 

 and they project as rounded tumors. Most 

 frequently new bone is formed beneath the 

 periosteum, so that the tumor is enclosed 

 in a thin, bony shell (Fig. 494) ; sometimes 

 there are also plates of bone in the tumor ; 

 sometimes the periosteum is unaltered; 

 sometimes it is perforated and the tumor 

 invades the surrounding soft parts. The 

 tumors are frequently very soft, vascular, 

 and hsemorrhagic in parts, or may enclose 

 cysts filled with tumor detritus and blood. 

 They are usually of the spindle or round- 

 celled variety, and not infrequently contain 

 giant cells. 



Sarcomata may originate in the outer 

 layers of the periosteum parosteaL They 

 may be as firmly connected with the bone 

 as is the periosteal form. The periosteum 

 may remain intact between the tumor and 

 the bone, or it may disappear and leave 

 them in apposition. Endothelioma of bone 

 is not uncommon. 



Angioma, A very large number of the 

 tumors which have been described under 

 this name are really very vascular sarco- 

 mata. Cavernous angiomata may form 

 between the periosteum and bone and inti- 

 mately connected with the latter. There are several cases described of 

 cavities filled with blood in the interior of bones, which it is difficult to 

 interpret. They have mostly been found in the head of the tibia. They 

 are said to have consisted of single sacs composed of thickened peri- 

 osteum, lined with plates of bone, and filled with fluid and clotted 

 blood. No large vessels communicated with the sacs, but their walls 

 were covered with a rich vascular plexus, branches of which opened into 

 the cavity of the sac. 



'See Wright, "Multiple Myeloma," Trans. Assn. Am. Phys., vol. xv., p. 137, 1900; 

 also Winkler,'V\rc\w\v'$ Arch., Bd. clxi., pp. 252, 508, 1900. 



FIG. 494. MYKLOGKNIC SARCOMA OF 

 THE STKRNUM. 



