SUPERNUMERARY TEETH. 271 



and fistula? form. The incisors are easily inspected, but examination 

 of the molars requires certain precautions varying in the different 

 classes of animals. Deviation of the teeth from their absolute or 

 relative positions likewise points to disease. With the assistance 

 of a mouth gag (Fig. 20) and the electric torch (Fig. 272a) the 

 crowns of the molars can be inspected in horses and cattle. 



Diseases of the teeth may be clinically divided into four groups : 



A. Irregularities in development. 



B. Irregularities in wear. 



C. Diseases of the tooth proper. 



D. Diseases of the alveolar periosteum. 



Fig. 272a.— Electric Torch. 

 (A) IRREGULARITIES IN THE DEVELOPMENT OF THE TEETH. 



EXTRA OR ADVENTITIOUS TEETH (POLYODONTIA, HYPERDENTITION). 



Kollmann states that in man during f cetal life more enamal germ 

 is sometimes formed than is required for the normal number of teeth, 

 and that this determines the production of supernumerary teeth. 

 Kitt looks on hyperdentition as a result of atavism, and points to 

 the fact that in former ages foals had more teeth than at present. 

 The same theory explains the appearance of the pre-molars in the 

 horse, whose ancestors (Hipparion, &c.) always had four pre-molars. 

 Kitt describes as a typical hyperdentition the apparently purposeless 

 excess of teeth, an example of which is cited by Goubaux, where a 

 certain horse had double the normal number of incisors. Gimther, 

 Stockfleth, and others have noted supernumerary molars. Their 

 commonest situation seems to be behind the third molar, but they 

 may lie alongside the normal teeth, being either in contact with the 

 tongue or cheek. At times milk teeth may be retained by becoming 

 fixed between their permanent successors. 



Supernumerary teeth are seen in most of the domestic animals, 

 supernumerary incisors, canines, and molars all being represented, 

 the latter most frequently. A regular series of such observations 



