TUMORS. 291 



lar bodies. Their shape and color are as variable as their size. 

 Epithelial or enamel odontomata are the highest in the scale of 

 hardness of all tumors. Other types of odontomata are soft. 

 Cystic odontomata may be single or multiple, as many as three 

 hundred having been observed in a single follicular tumor of 

 this type. They may grow very rapidly but more frequently 

 they develop slowly. They have no tendency to form metastases. 

 Degeneration is common in those developing from the tooth 

 follicle. Clinically they are benign but may cause fata! termina- 

 tion mechanically or from infection. 



According to the derivation .Sutton describes four classes of 

 odontomata as follows : 



1. Those derived from the enamel organ or epithelial odonto- 

 mata. They usually appear as irregular masses covered with 

 enamel. They may contain cystic cavities separated by enamel 

 partitions. Epithelial odontomata are usually surrounded by a 

 firm capsule, and in some instances appear to have had their 

 origin from a mucous membrane. Miscroscopicallv they are found 

 to be composed of enamel cells and irregular columns of epithe- 

 lial cells forming alveoli. The epithelial cells vary in shape from 

 columnar to the stellate or typical progenitors of enamel. These 

 tumors occur in most of the domestic animals and usually in 

 early life. Two epithelial odontomata were obtained from the 

 left maxillary sinus of an aged horse used for dissecting pur- 

 poses. These odontomata were completely enclosed in an osse- 

 ous mass, the maxillary sinus being completely filled by the new 

 growth. The facial bones were slightly bulged. The osseous 

 formation surrounding the odontomata and the thickening of the 

 facial bones indicated that considerable time had elapsed since 

 their formation. 



2. Those derived from the tooth follicle. Depending upon the 

 nature of the neoplasm this group mav be further subdivided 

 into follicular and fibrous odontomata, cementomata and com- 

 pound follicular odontomata. 



Follicular odontomata result from hyperplasia of the tooth 

 follicle tissues which thus prevents the normal eruption of the 

 tooth. They may appear as simple or multiple cysts. Their 

 walls may be calcareous or osseous but they are more frequently 

 membranous. The cysts are usually subdivided into many com- 

 partments, the cavities of which are lined with epithelium. This 

 lining epithelium secretes a viscid fluid, the accumulation of 

 which is responsible for the enlargement of the cysts. They 

 occur in sheep, hogs and horses. 



Fibrous odontomata are produced by a marked increase of 



