TUMOES. 



4. OSTEOMA. OSSEOUS TUMOR. 



489 



Osteoma is a solid tumor, composed of bone-tissue, and grow- 

 ing without symptoms of inflammation, in contradistinction to 

 the exostosis or the osteophytes, which are products of osteitis 

 and periostitis. Corresponding to the two principal varieties of 

 bone-tissue (see page 223), we have two kinds of osteoma : 



(a) Cancellous or EpipJiyseal or Spongy Osteoma. This occurs 

 on the epiphyseal ends of shaft-bones, closely connected with the 

 cancellous portion ; it is found only in youth, and is never a 

 primary formation after the thirtieth year of life. Such tumors 

 lie beneath the covering periosteum, and at their free surfaces 



FIG. 188. CANCELLOUS OR EPIPHYSEAL OSTEOMA, FROM THE 

 SECOND PHALANX OF THE THUMB. 



J 1 , trabeculae of bone-tissue, indistinctly lamellated; M, large and irregular medullary 

 spaces, containing blood-vessels and medullary tissue. (The latter shriveled, owing to the 

 circumstance that the specimen was brought for examination in a half-dry condition.) Mag- 

 nified 100 diameters. 



are usually lobular. They are either inclosed by a thin layer of 

 compact bone-tissue or by a layer of hyaline cartilage. They are 

 composed of indistinctly lamellated trabeculas of bone, contain, 

 ing regularly developed bone-corpuscles, and inclosing medullary 

 spaces, which vary greatly in size and are filled with medullary 

 tissue and blood-vessels. (See Fig. 188.) 



Formations closely allied to cancellous osteoma are the pro- 

 cessus supracondijloidei, which Hyrtl first described as congenital 



