il6 



THE DIGESTIVE APPARATUS IN MAMMALIA. 



originally secreted. The dental cavity gradually diminishes in extent ; the 

 papilla becomes atrophied, and finishes by disappearing altogether at a period 

 of life more or less advanced, according to the kind of teeth and species of the 

 animal. 



In considering the entire dental apparatus, with regard to its development, 

 very interesting differences are remarked in the progress and period of evolution 

 — differences which have been made available for ascertaining the age of animals, 

 but the details of which would be out of place here. It may only be noted that 

 all animals have two successive dentitions : the first, composed of a certain 

 number of teeth designated the caducous {temporary, deciduous, or milk-teeth — 

 cadiiques, decaying or frail), because they are soon shed and give place to others 

 which are stronger and more solid (and also because they appear while the 

 animal is yet sucking) ; the second, comprising the latter, are named replacing 

 teeth, with new, non-deciduous teeth which are not replaced, and are therefore 

 named persistent teeth. (The replacing and persistent teeth are generally included 

 by us in the term permanent.) 



The teeth of Solipeds are gradually pushed from their alveoli as they grow ; 



Fig. 229. 



y.^00 



THIN SECTION OF THE IXMER PORTION OF THE DENTINE AND OF THE SURFACE OF THE PULP 



OF AN INCISOR TOOTH. 



0, Portion in which calcification is complete, bhowing separate globular masses at the line of junction 

 with the uncalcified substance, 6 ; at c are seen oval masses of germinal matter (cells), with 

 formed material on their outer surface ; d, terminal portions of nerve-fibres. 



and from this circumstance results deformity and thinning of the maxillae in the 

 regions which lodge the roots of the teeth, 



B. Teeth of Solipeds. — The dentition of adult Solipeds is composed of 

 from 36 to 40 teeth, thus distributed in each jaw : male, 6 incisors, 2 canines, 

 12 molars ; female, 6 incisors, 12 molars.^ With regard to the first dentition, 

 it comprises the incisors and three anterior molars only, the canine teeth and 

 three posterior molars being persistent. 



The latter teetli — those of the second dentition — offer in their development 

 a common, but very remarkable character, rarely met with in the other animals. 

 They are pushed up from the alveoli during the entire life of the animal, to 



(' This is the number of persistent teeth given by all veterinary authorities, as well as 

 by Professor Owen. Huxley, however, gives the typical number in the ndult horse as forty-four. 

 The first premolar is supposed to be a perssisteiit, ami not a deciduous tooth, as it haa no 

 successor.) 



