TO THE LOWER ANIMALS 265 



same quality) may be found between the Gorilla's skull 

 and that of some other ape. So that, for the skull, no less 

 than for the skeleton in general, the proposition holds good, 

 that the differences between Man and the Gorilla are of 

 smaller value than those between the Gorilla and some 

 other Apes. 



In connection with the skull, I may speak of the teeth 

 organs which have a peculiar classificatory value, and 

 whose resemblances and differences of number, form, 

 and succession, taken as a whole, are usually regarded 

 as more trustworthy indicators of affinity than any 

 others. 



Man is provided with two sets of teeth milk teeth and 

 permanent teeth. The former consist of four incisors, or 

 cutting teeth ; two canines, or eye-teeth ; and four molars, 

 or grinders, in each jaw making twenty in all. The 

 latter (Fig. 17) comprise four incisors, two canines, four 

 small grinders, called premolars or false molars, and six 

 large grinders, or true molars, in each jaw making thirty- 

 two in all. The internal incisors are larger than the 

 external pair, in the upper jaw, smaller than the external 

 pair, in the lower jaw. The crowns of the upper molars 

 exhibit four cusps, or blunt-pointed elevations, and a 

 ridge crosses the crown obliquely, from the inner, anterior, 

 cusp to the outer, posterior cusp (Fig. 17 m 2 ). The anterior 

 lower molars have five cusps, three external and two internal. 

 The premolars have two cusps, one internal and one external, 

 of which the outer is the higher. 



In all these respects the dentition of the Gorilla may be 

 described in the same terms as that of Man ; but in 

 other matters it exhibits many and important differences 

 (Fig. 17). 



Thus the teeth of man constitute a regular and even 

 series without any break and without any marked pro- 

 jection of one tooth above the level of the rest ; a peculiarity 

 which, as Guvier long ago showed, is shared by no other 

 mammal save one as different a creature from man as can 

 well be imagined namely, the long extinct Anoplotherium. 

 The teeth of the Gorilla, on the contrary, exhibit a break, 

 or interval, termed the diastema, in both jaws : in front 

 of the eye-tooth, or between it and the outer incisor, in 

 the upper jaw ; behind the eye-tooth, or between it and 

 the front false molar, in the lower jaw. Into this break in 

 the series, in each jaw, fits the canine of the opposite jaw ; 



