THE TEETH OF MAN. 



('Anatomy of the Facial Region'), "if the hairs of the 

 scalp were to be inserted into the skull, or of the moustache 

 into the upper jaw, we should express great astonishment, 

 yet such an extreme proposition is no more remarkable than 

 what is seen to take place in the jaws," again " the feathers of 

 certain birds making impressions on the radius, the whalebone 

 pendent from the roof of the mouth, are examples of this 

 same association of tegumentary appendages with the 

 bones." 



In their simpler forms, then, teeth are met with as very 

 numerous spines, differing but little from the spines of the 

 skin except in size, and still less from one another. In 

 many fish the teeth, though more specialised, are scattered 

 over almost every one of the numerous bones which form 

 part of the walls of the mouth and pharynx ; in reptiles 

 they are much more limited in position, and in mammals 

 are absolutely confined to the intermaxillary, maxillary, 

 and mandibular (lower maxillary) bones. In fish and rep- 

 tiles it is the exception for the teeth in different parts of 

 the mouth to differ markedly from each other; in mam- 

 mals it is the rule. 



Teeth owe their hardness to an impregnation with salts 

 of lime ; the organic matrix may be of albuminoid charac- 

 ter, in which case the tooth is of horny consistence, and is 

 spoken of as " cornified ; " or the matrix may be, like that 

 of bone, gelatigenous, in which case the tooth is more richly 

 impregnated with salts, and is spoken of as " calcified." 



The great mass of a calcified tooth is usually made up of 

 "dentine," which gives to it its characteristic form, and 

 often practically constitutes the whole tooth : to this may 

 or may not be added enamel and cementum. 



Without further prelude we may pass to a description of 

 the human teeth, this course appearing to me, after some 

 little consideration, to afford to the student the most ad- 



B 2 



