The Head and Neck 85 



As the animal ages the prominences of the molars are worn 

 away, only the largest tubercles remaining. The posterior face of the 

 lower canine impinges against and abrades the anterior face of the 

 upper, in front of which it closes. The anterior face of the lower 

 canine also comes in contact with the corner incisor and an abrasion 

 takes place at this point. The older the animal the more apparent 

 are these abrasions. The crowns of the incisors become much re- 

 educed in size in aged animals, mere stumps remaining after eight 

 or ten years, while they are completely worn away after ten or 

 twelve years, or the whole tooth may be shed, together with the 

 first premolar. Gradual discoloration talces place in late years. 



CONGENITAI, MALFORMATIONS. 



Certain breeds possess defective atypical dentition. This pecu- 

 liarity was referred to by Darwin and Magitot. The breeds invari- 

 ably having imperfect dentition are the Chinese, Turkish, and Mex- 

 ican Hairless. The phenomenon is not to be wondered at when it 

 is remembered that the teeth and dermis have a common epiblastic 

 origin. Individual members of the Mexican breed examined by 

 Waugh were found to have the tricuspid arrangement of the in- 

 cisors wanting, absence of the canines, and slower and later develop- 

 ment of the molars than other breeds. Half-breeds had canines 

 in the upper or lower jaw but not in both jaws. In several members 

 of both sexes of this breed that I have had the opportunity to ex- 

 amine I have found the arrangement generally as follows: In the 

 upper jaw there is a reduced number of rudimentary or fairly well- 

 developed incisors, but without the cuspid arrangement. Well-de- 

 veloped canines are in evidence, and on either side well-developed 

 first premolars and first molars, the animals being thus minus the 

 superior sectorials. In the lower jaw the incisors are developed 

 in about the same degree as those of the upper, but the canines 

 are less constant and sometimes entirely absent. Premolars are also 

 inconstant but first and second molars are often present showing 

 the inferior sectorials to be intact. When the molars have no teeth 

 to oppose them they may cause the formation of indentations in the 

 opposite jaws. As is natural to expect, these animals do not care to 

 eat hard foods, but prefer slops and soft bread and cakes. Meat can 

 only be swallowed if cut fine, as they are without the ability to re- 

 duce the size of tough or hard articles of diet, which dogs with nor- 



