CRUSTA-PETBOSA TUMOURS. 



435 



VI. — CRUSTA-PETROSA TUMOURS. 



Fig. 105. 



The above 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^. 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 G. 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 hypertrophy 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- 

 tum is in every way similar in structure to that previously form- 

 ing part of the tooth." He again says — "In dental exostosis 

 the amount of new cementum may be very slight, or may be 

 considerable in quantity. The affected fang may be but little 

 enlarged, or it may be increased to twice its natural size. Near 

 about the end of the fang is the most common situation to find 

 the greatest amount of cementum ; but you seldom find an 



