90 



TOPOGRAPHICAL ANATOMY OF THE 



possession of an auterior border iustead of a surface of contact. The 

 first tooth also differs in the character of its buccal surface. In the 

 second to the sixth tooth, this surface carries a longitudinal, rounded 

 ridge that separates two grooves. In the first tooth there are two such 

 ridges, the anterior being somewhat the less prominent. The lingual 

 surface of the crown of each tooth is marked by a longitudinal ridge, 

 agreeing in position with a column or pillar, presently to be noted in 

 connection with the chewing surface, defined by a groove on each side. 



It will be readily observed that the crowns of the maxillary cheek- 

 teeth are taller towards the buccal surface than they are on that side 

 which is in contact Avith the tongue. In other words, the chewing sur- 

 face is not at right angles to the longitudinal or vertical plane of the 

 tooth, but is set obliquely thereto. A similar feature will also be noted 

 in connection with the mandibular teeth. 



Cement. 



Enamel. 



Fig. 33. 



Dentine. 



-Diagram of the chewing surface of a 

 raaxillarv cheek-tooth. 



The chewing surface is very characteristic. Owing to deep and 

 complicated folding of the enamel, the unworn tooth presents a surface 

 on which there are two undulating and narrow ridges — one lateral and 

 the other medial — to the anterior and lingfual side of the medial of 

 which an extra hillock (column or pillar) is added. The central portion 

 of the surface is indented by two depressions (anterior and posterior) 

 comparable to, but much deeper than, the infundibula of the incisor 

 teeth. When the teeth have been subjected to wear, the enamel 

 clothing the ridges is worn through, and the underlying dentine appears 

 on the surface. The result is that after a time the chewing surface dis- 

 plays a complicated pattern that may be likened to the outline of an 

 ornamental and ornate capital letter B, to the upper curve of which an 

 appendix (the extra column above referred to) has been added. It will 

 be observed that both in the infundibula and on the surface of the 

 crown cement is abundant. 



