86 Surgical Diseases and Surgery of the Dog 



mal mouths accomplish by the scissor-like movements of their 

 sectorials. 



In all breeds the deciduous teeth sometimes persist, while su- 

 pernumerary teeth, usually molars, are not uncommon. As a rule, 

 the larger breeds have a full complement of teeth, while the smaller 

 ones often lack the third molar of the lower jaw. 



The teeth may occupy anomalous positions. Distortion of the 

 bones of the skull may throw the opposing jaws out of their proper 

 relationship ' so that the teeth cannot meet. An instance of such 

 deformity was witnessed by Gurlt. 



Dentigerous Cysts. Through inclusion of epiblastic tissue dur- 

 ing fetal development teeth may occupy obscure positions. These 

 sequestered teeth have been found in the ovaries but their occur- 

 rence is perhaps more common in the temporal region, where they 

 give rise to cystic formation. Instances have been observed by 

 Werwey and Cadiot and Almy. Such cysts ordinarily remain quies- 

 cent but if pyogenic microorganisms gain entrance into their interior 

 inflammation takes place and a fistula results having its orifice of 

 discharge within the auditory canal. Its presence is first made 

 known by the appearance during the early months of life, particularly 

 about the period of dentition, of a soft, insensitive, hemispherical 

 tumor, which may persist as such or become fistulous. 



Treatment. The proper treatment is complete extirpation of 

 the cyst as it is liable to return if any portion of the wall is allowed 

 to remain. If a tooth is found present it should be extracted. In 

 Cadiot and Almy's case simple extraction of the tooth was all that 

 was necessary and healing was complete within a month. 



TRAUMATIC LESIONS. 



Fracture with exposure of the pulp sometimes occurs in a me- 

 chanical way, being generally sustained during a fight or from at- 

 tempted extraction by inexperienced hands. Darwin has remarked 

 that wild camivora kept in cages frequently sustain fracture of the 

 teeth through their habit of seizing the bars, and so we find to be 

 the case in dogs under similar conditions. Dogs in jumping over 

 iron fences sometimes get caught in the railing or are impaled, and 

 in their attempts to break loose, tear at the iron with their teeth, 

 and thus sustain fracture. Some animals have naturally brittle teeth 

 which are fractured with very little force, while others suffer from 



