DISSECTION OF THE DOG 171 



by the lips or cheek (facies labialis, facies buccalis), and a surface looking 

 towards the tongue (facies linguaUs). Generally a tooth touches its neighbour 

 by a surface of contact (facies contactus). All except old teeth contain a cavity 

 (cavum dentis) entered by an opening at the apex of the root (foramen apicis 

 dentis) and containing the tooth pulp (pulpa dentis). 



With the naked eye it is possible to distinguish three tissues forming a tooth. 

 Dentine (substantia eburnea) constitutes the greater part of the structure. 

 Enamel (substantia adamantina) forms a porcelain-like white cap covering the 

 crown ; and cement (substantia ossea), a bone-like tissue, covers the roots and 

 possibly also parts of the crown. 



Teeth are classified from before to behind as incisors (dentes incisivi), 

 canines (dentes canini), premolars (dentes praemolares) , and molars (dentes 

 molares). When complete, the dentition of the adult dog comprises forty- two 

 permanent teeth (dentes permanentes) , of which twelve are incisors, four 

 canines, sixteen premolars, and ten molars. The permanent dental formula of 

 the dog is |-}||-, from which it is evident that the upper and lower rows of 

 teeth are not numerically equal. Each maxillary bone carries only two 

 molars, whereas each half of the mandible has three. 



The incisor teeth are placed close together and increase in size from the first 

 to the third. The mandibular teeth are smaller than those in the incisive 

 bones. The crown of each incisor presents three projections, and on the 

 lingual surface there is a curved ridge, the cingulum, close to the neck. 



The canine teeth are large, with conical, curved crowns. A cingulum is 

 present, as it is on all the teeth. The upper tooth is separated by a gap from 

 the third incisor, and a similar interval separates the lower canine from the 

 first premolar. These gaps receive the opposed tooth when the mouth is 



closed. 



The premolar teeth increase in size from the first to the last. The first is 

 small and has only one root. The second and third in the maxilla, and the 

 second, third, and fourth in the mandible have two roots. The last premolar 

 in the maxilla is much larger than the others and has three roots. It is 

 distinguished by the name of sectorial or carnassial tooth. 



The two molar teeth in the maxilla have broad, hregularly triangular and 

 tubercular chewing surfaces, and each has three roots. The s;cond tooth is 

 much the smaller. 



The first mandibular molar is much larger than its neighbours and forms 

 the sectorial tooth of the lower row. Its crown is similar to that of the last 

 upper premolar. The second and thhd mandibular molars have tubercular 

 chewing surfaces, and the third is smaller than the second. The first and 

 second molars have two roots, but the last has only one. 



Palatum dttbtim.— The hard palate consists of a dense mucous membrane, 

 with a very vascular deep layer, attached to the periosteum of the palatme, 

 maxillary and incisive bones. An indifferently marked median, longitudinal 



