288 



VETERINARY PATHOLOGY. 



OSTEOAIA. 



An osteoma is a tumor composed of osseous tissue. Pure 

 osteomata are not common. They occur most frequentl_v in re- 

 lation to bones and usualh^ at tb.e union of osseous tissue devel- 

 oped from different ussifying centres. These tumors are quite 

 common in mules, appearing as projecting pedunculated masses 

 attached to tlie inferior maxilla. More rarely they are found in 

 other organs, as the lung, parntid gland, mammary gland, etc. 



Fig. 146. — redirnculated Osseous Tumor Maxilla. Horse. 



These tumors are iisuallv small, rarely becoming as large as 

 a cocoanut. The}- are hard, nodular masses that are fre(|uently 

 lobulated and usually firmb- attached to the surrounding tissue. 

 It is possible that they are developed from osseous cells which 

 have been misplaced in bone formation or from the osteogenetic 

 layer of the i)eriostcum. AVhen thev develo]:i adjacent to pre- 

 existing bone the periosteum or endosteum surrounds them. 

 Thfise osteomata develnping in other structure than bone arc 

 surrounded b\- a distinct mem1)rane which is usually very sim- 

 ilar to periosteum. ( Jsteomata may be classified as: (1) hard, 

 ivory or eburnated, and i'i) snft, spongy or cancellated. Either 

 of the foregiting classes may 1)e homnhigous or heter( ilogotis. 

 Homologrius fisteomata occur in bony structures and may be an 

 exostosis or an enostosis. Heterologous osteomata occur in other 

 tissue than bone. 



Hard, i\-or\- or eburnated osterimata are structurally very 

 similar to the compact risserius tissue of a long bone. Haversian 

 systems may 1:ie present or they may 1)C absent. Tf the Ha\'ersian 

 systems are present they are irregularly arranged and are ap- 

 prnximately perpendicular tri tlie surface of the related bone. If 



