92 



TOPOGRAPHICAL ANATOMY OF THE 



plane of the tooth. Apart altogether from any structural arrangement, 

 the maintenance of the slope on the chewing surfaces of the maxillary 

 and mandibular teeth can be associated with the fact that the maxillary 

 teeth of the two sides of the head are farther apart than are the two 

 rows of mandibular teeth. 



The pattern assumed by the worn dental tissues on the mandi- 

 bular teeth is different from and simpler than that of the maxillary 

 teeth ; for, while there are two infundibula, these are not closed on the 

 lingual side until cement has been extensively developed. The conse- 

 quence is that in the worn tooth the enamel fold lingual to each 

 infundibulum is incomplete. 



First maxillary molar. 



Second maxillary premolar. 

 First maxillary premolar. 



First mandibular molar. 



I Incisors. 

 I Canines. 



Second mandibular premolar. 



Fk;. 35. — The teeth after their embedded parts have been exposed by 

 removal of the surrounding bone. 



With the exception of the last, which has usually three, each of the 

 mandibular cheek-teeth has two relatively short roots. 



The first mandibular tooth is implanted in the jaw at right angles 

 to the lower border of the mandible. The implantation of the rest of 

 the teeth is oblique (downwards and backwards), the obliquity gradually 

 increasing from the second to the last. 



The deciduous premolars are smaller than their representatives in 

 the permanent dentition, their crowns are shorter, and a neck may be 

 recognised. 



Dissection. — The tongue, pharynx and larynx should now T)e removed, 

 in order that an examination of tlie last-named may he proceeded with. 

 In the first place, the thyro-hyoid and transverse hyoid muscles nuist be 

 cleaned and defined. 



M. THYREOHYOIDEUS. — The thyro-hy'oid is a broad, flat muscle aris- 

 ing from the body and thyroid process of the hyoid bone, and inserted 



