Chap. IV.] MANNER OF DEVELOPMENT. 121 



In man the canine teeth are perfectly efficient instru- 

 ments for mastication. But their true canine character, as 

 Owen^" remarks, "is indicated by the conical form of the 

 croAvn, which terminates in an obtuse point, is convex out- 

 ward and flat or subconcave within, at the base of which 

 surfoce there is a feeble prominence. The conical form is 

 best expressed in the Melanian races, especially the 

 Australian. The canine is more deeply implanted, and by 

 a stronger fang, than the incisors." Nevertheless this tooth 

 no longer serves man as a special weapon for tearing his 

 enemies or prey ; it may, therefore, as far as its proper 

 function is concerned, be considered as rudimentary. In 

 every lai'ge collection of human skulls some may be found, 

 as Hackel*" observes, with the canine teeth projecting 

 considerably beyond the others in the same manner, but 

 in a less degree, as in the anthropomorphous apes. In 

 these cases, open spaces between the teeth in the one jaw 

 are left for the reception of the canines belonging to the 

 opposite jaw. An interspace of this kind in a Kaffir skull, 



to this through Prof. Owen's statement, that some of the Ichthyopterygia 

 possess more than five digits, and therefoi'e, as I supposed, had retained 

 a primordial condition; but after reading Prof. Gegeubaur's paper 

 (' Jenaischen Zeitschrift,' B. v. Heft 3, s. 341), who is the highest author- 

 ity in Europe on such a point, and who disputes Owen's conclusion, I see 

 that it is extremely doubtful whether supernumerary digits can thus be 

 accounted foi". It was the fact that such digits not only frequently occur 

 and are strongly inherited, but have the power of regrowth after amputa- 

 tion, like the normal digits of the lower vertebrata, that chiefly led me to 

 the above conclusion. This extraordinary fact of their regrowth remains 

 inexplicable, if the beUef in reversion to some extremely remote pro- 

 genitor must be rejected. I cannot, however, foUov/^ Prof. Gcgenbaur in 

 supposing that additional digits could not reappear through reversion, 

 without at the same time other parts of the skeleton being simultaneous- 

 ly and similarly modified ; for single characters often reappear through 

 reversion. 



33 'Anatomy of Vertebrates,' vol. iii. 1868, p. 323. 



*^ 'Gencrclle Morphologic,' 1866, B. ii. s. dv. 



