160 THE STRUCTURE OF MAN 



in Man, and Eose has since proved that this vestige is on each 

 side coincident with the end of the epithelial dental ridge. 



By milk teeth are usually understood the first formed 

 generation of teeth. Eose, however, has recently attempted to 

 show that the milk teeth do not correspond with the first series 

 of teeth of the lower Vertebrates, and that they cannot be 

 homologised with any one special series in Eeptiles and allied 

 forms. Milk teeth, according to him, must rather be considered 

 to have arisen by the concrescence of several consecutive 

 generations of teeth of our ancestors, into one single, more solidly 

 constructed, series, the sum of all the remaining rows which were 

 once present having been in Man, as in all diphyodont Mam- 

 mals, compressed into the second or permanent series. [This 

 is, however, but one of several views put forward during recent 

 years on the subject of the Mammalian tooth genesis. Much 

 more important is the fact that, in Man, while the premolars 

 are comparatively simple teeth, the milk molars which precede 

 them are more complex, and more conformable, in the characters 

 of their fangs and crowns, to the type of the true molars. 

 These facts suggest that the deciduous (milk) molars are of a 

 more primitive (i.e. a less reduced) type than the successional. 1 ] 



Until quite recently, the possibility of Man's developing a 

 third dentition was generally denied, but it is now proved that 

 that may sometimes occur. Baume, Zuckerkandl, and Eose, have 

 discovered a third set of enamelless tooth rudiments on the outer 

 or labial surface of the jaw, [and Schwalbe has lately suggested 2 

 that they may be the vestiges of a distinct pre-milk dentition, 

 of which traces have been found by Kiikenthal in the Seal, by 

 Nawroth in the Pig, and, in a more extensive and calcified form, 

 by Leche in the Banded Ant-Eater (Myrmecobius}. Great 

 interest attaches to further inquiry into these structures.] 



In Fishes, Amphibians, and some Eeptiles, the first formed 



1 [A very interesting allied case is furnished by the common Dog. In the upper 

 jaw of that animal, the characters of the fourth milk (deciduous) molar are almost 

 exactly those of the first true molar, and the characters of the third milk molar those 

 of the fourth premolar. Similarly, the second and first milk molars closely resemble 

 the third and second premolars, allowance being in all cases made for mere differ- 

 ence in size. Indeed, comparison of the premolars with the milk molars and, through 

 these, with the first molar, reveals a marvellous series of progressive stages in 

 simplification and reduction of the type of tooth represented in the adult dentition 

 by the first upper molar. I am hoping shortly to have this most important matter 

 fully worked out in detail. G. B. H.] 



2 [Cf. Schwalbe, Morph. Arbeiten, Bd. iii. p. 531, and Nawroth, "Zur Ontogenese 

 d. Scheweinemolaren," Inaug. Dissert. Basel, Berlin, 1893.] 



