62 Mammalia. Digestive System. 



and Mandibular or lower maxillary bones, and form a single 

 row in each : they may be a- symmetrical, either as comparing 

 one jaw with the other, or even one side of the same jaw with 

 the other, though this is rare. When there is but one fully 

 developed tooth* it is never median. The teeth never all make 

 an unbroken series in any existing f Mammal save in man. 

 Those teeth which are implanted in the Premaxillary bones 

 and in the corresponding part of the lower jaw are called 

 * Incisor a J* whatever their shape or size: the tooth in the 

 Maxillary bone which is situated at, or near to the suture 

 with the Premaxillary is the * Canine,^ as is also that tooth 

 in the lower jaw which, in opposing it, passes in front of its 

 crown, when the mouth is closed : posteriorly to these are 

 situated, in the Deciduous dentition, the ^Milk Molars '; and in 

 the Permanent dentition, the Premolars (succeeding the Milk 

 Molars) and the true Molars (without predecessors). Fixation. 

 In no Mammal does anchylosis of the tooth xcith the jaw con- 

 stitute a normal mode of attachment. Each tooth has its 

 particular Socket, to which it firmly adheres, by the close 

 coadaptation of the apposed surfaces, and by the firm ad- 

 hesion of the alveolar periosteum to the organised Cement 

 which invests the fang or fangs. The complicated form of 

 Socket which results from the development of two or more 

 Fangs is peculiar to species of the class Mammalia. Form. 

 Three parts are generally recognisable in a Mammalian tooth ; 

 the FangX, or E-oot, the inserted part ; the Crown, or exposed 

 part ; and the Neck, or constriction which divides the Fang 

 from the Crown. It is peculiar to this Class to have teeth 

 with two or more Fangs wherewith to be implanted in 

 Sockets ; but Fangs are not always present : for there are 



* Narwhal. 



t In Anoplotherium, Nesodon, and Dicliodon the teeth are said to have formed 

 an unbroken series. 



X The term Fang is properly given only to the implanted part of a tooth of 

 restricted growth, which fang gradually tapers to its extremity. 



