CRUSTA-PETROSA TUMOUES. 



419 



The only change that occurs in these tuniours is their ossifica- 

 tion into a cancellous structure enclosed in a thin compact shell 

 of bone. I have never seen the fatty degeneration or cystic 

 transformation spoken of by human pathologists ; but it is quite 

 possible that such a change may occur. 



Tia. 83. 



Fio. 84. 



I'los. 83 and 84. — Enchondroma. Flo. 83. Structnre of a firm enchondroma. - 

 The right of the figure represents, above, mineral deposit in and around the cells ; . 

 and, below, some isolated cartilage corpuscles. Fio. 84. The same, after the 

 addition of acetic acid, rendering the Whole — and especially the nucleus — more 

 transparent. 25X) diam. — (Bennett.) 



Treatment. — The only method is their removal by excision,- 

 and that as early as possible. 



VI. — CRUSTA-PETROSA TUMOURS. 



The following drawing represents a section of a tumour "now in 

 the Veterinary College Museum, composed- of crusta-petrosa, 

 attached to one of the molars of the ox. I have no history of 

 the case ; but upon examination find that the attached tooth is 

 the last molar of the upper jaw. 



At A. the tooth is represented with its table running obliquely 

 downwards towards C, and its crown lost in the adventitious 

 substance. B. The shining surface of the section, and C. the 

 crown surface of the tumour, slightly worn upon its inferior 

 aspect by contact with the teeth • of the opposing jaw. The 

 tumour weighs 1 lb. 3 oz. 



Tomes describes a similar condition 'of the crusta-petrosa under 

 the term dental exostosis or hj'pertrophy of the cementum, and 

 he says — " It will not be forgotten that the surfaces of the fangs 

 of teeth are coated with a thin layer of cementum. Under 

 certain circumstances this layer becomes increased in thickness 

 by additions on the external surface. The newly added cemen- 



