66 THE HUMAN SPECIES 



organisation, so also he considers that the human teeth are 

 among the most primitive possessed by any of the existing 

 mammals. Had man not sacrificed twelve teeth in the course 

 of his gradual development, he would now have forty-four, the 

 largest number possessed by any land-dwelling mammal. One 

 of the most important points in classifying man in the order 

 of animals is, in the opinion of Klaatsch, the four-cusped human 

 molar. Now as the arctocyon and the Phenacodus (a member of 

 the Ungulata) of the Eocene Period possessed molar teeth which 

 resemble man's as closely as man's resemble those of the anthro- 

 poids, Klaatsch concludes that man, as regards his molar teeth, 

 has not progressed beyond the stage of development reached by 

 the mammals in the Tertiary Period. Further proofs must be 

 produced in connection with other organs of the human body. 

 Wiedersheim l has pointed out that the teeth of the higher 

 vertebrates show interesting signs of reversion. In fishes, 

 amphibians, and certain reptiles the first signs of teeth are 

 epithelial formations which later become absorbed into the 

 mesoderm and form the teeth-ridges, and these develop in due 

 course into the actual teeth. The higher vertebrates have also 

 in the first place similar teeth-ridges but without the pre- 

 liminary formation of papillae. Rose, however, has found that 

 in the human embryo a transitionary formation of rudimentary 

 papillae precedes the formation of the teeth-ridges. 



Vertebral Column. 



In the fishes, batrachians, and reptiles, the division of the 

 body into distinct regions is rudimentary, first being perfected 

 in the birds ; the vertebral column in birds, and in mammals, 

 differs conspicuously as to the number of separate vertebrae. 



Man alone (see Fig. 21) possesses a fixed number of verte- 

 brae. Birds have frequently very numerous cervical and lumbar 

 vertebras, and in mammals the figures are as follows : 

 12 to 23 dorsal vertebrae 



3 to 7 lumbar vertebras 



2 to 5 forming the sacrum 



4 to 46 caudal vertebrae 

 7 cervical vertebrae 



1 R. Wiedersheim, loc. cit., p. 172. 



