DECIDUOUS TEETH. 



1121 



1st molars appear soon after the 6th year. 

 Central incisors appear soon after the 7th year. 



Lateral 



1st pre molar 



2nd 



Canine 



2nd molar 



3rd 



from the 



8th 

 9th 

 10th 

 llth 

 12th 

 17th 



to 21st year, or even later. 



Variations in the Number of the Teeth. The presence of an additional tooth is by no 

 means uncommon. It may appear in connexion with the incisor, premolar, or the molar groups. 

 A distinction is drawn between " supernumerary " or imperfect additions to the dentition and 

 "supplemental" teeth which correspond in size with those with which they are associated. 

 When a supplemental incisor appears it has an interesting bearing upon the solution of the 

 much -debated point as to which incisor has disappeared from the primate dentition. A 

 fourth molar is occasionally present. 



DENTES DECIDUI. 



temporary or milk) are twenty in number, 

 five in each half of each jaw namely, two 



1st molar 



Canine 



Lateral incisor 

 Central incisor 



The deciduous teeth (O.T. 

 ten above and ten below, or 

 incisors, one canine, and two 

 i molars. They may be dis- 

 tinguished from the permanent 

 teeth by their smaller size, 

 their well-marked and con- 

 stricted necks, and, in the case 

 of the molars, by the wide 

 divergence of their roots (Fig. 

 887). Otherwise they corre- 

 spond so closely to the same- 

 named teeth of the permanent 

 set, that they require no separ- 

 ate description, except in the 

 case of the molars. The first 

 upper molar has but three 

 tubercles on its crown two 

 labial and one palatal ; the 

 first lower molar has four 

 two labial and two lingual, 

 and the crowns of both are 

 flattened from side to side. 

 The second molars of the max- 

 illa have four, those of the 

 mandible five tubercles each. 

 In every case the second are 

 much larger than the first 

 molars. The tubercles are sharper and are separated by deeper fissures or fossae 

 than those of the permanent teeth, whilst the roots of the deciduous molars, 

 except for their greater divergence, agree with those of the permanent set. 



The marked constriction at the neck of the deciduous teeth (Fig. 887) is due to a great thicken- 

 ing of the cap of adamant on the crown, and its abrupt termination as the neck is reached. The 

 adamant, too, is much whiter as a rule than in the permanent teeth. It should be added 

 that the labial surface of the canines and molars departs very markedly from the vertical ; 

 ' slopes strongly inwards towards the mouth cavity as it approaches the masticatory surface of 

 the crown, which latter is, as a result, much reduced in width. 



The divergence of the roots in the deciduous molars allows the crowns of the permanent pre- 

 molars to fit in between them before the former molars are shed. 



2nd molar 



2nd molar 

 crown 



1st molar 

 FIG. 887. THE DECIDUOUS TEETH OF THE LEFT SIDE. 



The masticating surfaces of the two upper molars are shown above. 

 In the second row the upper teeth are viewed from the outer 

 or labial side. In the third row the lower teeth are shown 

 in a similar manner ; and below are the masticating surfaces 

 of the two lower molars. In the specimen from which the 

 first upper molar was drawn the two labial tubercles were not 

 distinctly separated, as is often the case. 





