3G2 



THE DIGESTIVE APPARATUS IN MAMMALIA. 



After their complete eruption from the alveolar cavities, the Dog's teeth are no longer 

 pushed outwards. They are remarkable for their brilliant whiteness, which they owe 

 to the absence of cement on their covering of enamel. 



The Cat has thirty teeth : twelve incisors, four tusks, and fourteen molars, eight of 

 which are in the upper, and six in the lower jaw. 



All these teeth are constructed on the same type as those of the Dog. The tusks are 

 deeply striated on their external surface, instead of being smooth. 



(The importance of a correct knowledge of the period of eruption, shedding, replacing, 

 and general wear of the teeth of the domesticated animals, as a guide to their age', 

 induces me tc give the table on pa^e 363 (from Leyh), as indicating at a glance the age 

 at which the teeth appear, are shed, and replaced in the different creatures: 



Baumeister divides the successive evolutions in the wear of the tables of the Horse's 

 incisor teeth into four periods from six years to extreme old age. The first, the trans- 

 versely-oval period, extends from six to twelve years ; the round, from twelve to 

 eighteen years ; the triangular, from eighteen to twenty-four years, and the antero- 

 posterior oval or triangular, from twenty-four years and upwards. Girard and other 

 French authorities shorten these periods somewhat. The triangular period, for instance, 

 only lasts from fourteen to seventeen years.) 



COMPARISON OF THE MOUTH OP MAN WITH THAT OF ANIMALS. 



The brevity of Man's face influences the shape of the mouth ; therefore it is propor- 

 tionally shorter and wider than in the domesticated mammals. 



Fig. 168. 



MEDIAN ANTERO-POSTERIOR SECTION OF THE HUMAN FACE. 



a, Septum of nose, with section of hard palate below it ; b, Tongue ; c, Section of 

 soft palate ; d, rf, Lips ; ?/, Uvula ; r, Anterior arch, or pillar of fauces ; ', Pos- 

 terior arch ; t, Tonsil ; p, Pharynx ; /i, Hyoid bone ; , Thyroid cartilage , n, Cricoid 

 cartilage ; s, Epiglottis ; v, Glottis ; 1, Posterior opening of nares ; 3, Isthmus 

 faucium ; 4, Superior opening of larynx j 5, Passage into oesophagus ; 6, Orifice 

 of right Eustachian tube. 



