DEVELOPMENT OF THE TEETH IN MAMMALIA 43 



As it is generally allowed that subsidiary cusps arise 

 from the cingulum, Bolk's views would appear to combine 

 to some degree three principal views of cusp development 

 concrescence, trituberculy, and the cingulum theory. 



The structures described by this author in the enamel 

 organ are of great interest in their bearing on tooth develop- 

 ment, and the confirmation of their constant presence in 

 early tooth germs would be of great value in the explanation 

 of the evolution of the teeth of primates. 



The subject is such a complicated one, especially in 

 determining the homologies of the ungulate molar, and 

 there are so many side issues connected with it, that it is 

 impossible to give anything but the merest outline in 

 a work of this scope, but the author has endeavoured to 

 state as simply as possible the principal views with regard 

 to the evolution of the human molar. 



The reader who wishes to pursue this interesting subject 

 further is referred to the works mentioned in the short 

 bibliography attached to this chapter, and especially to 

 Osborn's Evolution of Mammalian Molar Teeth. An interest- 

 ing paper on the evolution of human dentition by Mr. John 

 Humphreys was contributed to the Sixth International 

 Dental Congress (9). 



REFERENCES 



1. Ameghino, F. (a) Filogenia, 1884. 



(6) 'On the Primitive Type of the Plexodont Molars of Mammals.' 



Proc. Zool Soc. Lond., 1899. 

 (c) ' Sur 1'evolution des dents des mammiferes.' Bol Acad. Nac. 



Ciencias en Cordoba, t. xiv, 1896, pp. 381-517. 



2. Baume. ' Versuch einer Entwickelungsgeschichte des Gebisses.' 



Odontologische Forschungen, 1882. 



3. Bolk, L. (a) 'The Structure of the Reptilian Dentition and its Rela- 



tionship to the Mammalian Dentition.' Anai. Anzeig., vol. xli, 

 Supplement, Berlin, 1912. 



(6) Die Ontogenie der Primatenzdhne (Odontolog. Studien, I): Versuch 

 einer Lo'sung der Gebissprobleme, 122 pp., Jena, 1913. 



4. Cope, E. D. (a) ' Systematic Catalogue of the Vertebrata of the 



Eocene of New Mexico.' Rept. Geog. Explor. and Surveys, <bc., 

 Wheeler, 1875, pp. 5-7. 



(6) ' On the Trituberculate Type of Molar Tooth in the Mammalia.' Pall. 

 Bull., No. 37, Proc. Amer. Phil. Soc., xxi, December 1883, pp. 324-6. 



