1114 



SPLANCHNOLOGY 



The dental formulae may be represented as follows: 



Deciduous Teeth. 



Upper jaw 



mol. can. in. in. can. mol 



2 2 



1 



Lower jaw 



Total 32 



1 



2 2 



1 



General Characteristics. Each tooth consists of three portions: the crown, 

 projecting above the gum; the root, imbedded in the alveolus; and the neck, the 

 constricted portion between the crown and root. 



FIG. 998. Maxillae at about one year. (Noyes.) 



The roots of the teeth are firmly implanted in depressions within the alveoli; 

 these depressions are lined with periosteum which invests the tooth as far as the 

 neck. At the margins of the alveoli, the periosteum is continuous with the fibrous 

 structure of the gums. 



In consequence of the curve of the dental arch, terms such as anterior and 

 posterior, as applied to the teeth, are misleading and confusing. Special terms 

 are therefore used to indicate the different surfaces of a tooth : the surface directed 

 toward the lips or cheek is known as the labial or buccal surface; that directed 

 toward the tongue is described as the lingual surface; those surfaces which touch 

 neighboring teeth are termed surfaces of contact. In the case of the incisor and 

 canine teeth the surfaces of contact are medial and lateral; in the premolar and 

 molar teeth they are anterior and posterior. 



The superior dental arch is larger than the inferior, so that in the normal condi- 

 tion the teeth in the maxilla? slightly overlap those of the mandible both in front 

 and at the sides. Since the upper central incisors are wider than the lower, the 

 other teeth in the upper arch are thrown somewhat distally, and the two sets do 



