CHAPTER III. 



TRITUBERCULY IN RELATION TO THE HUMAN MOLAR TEETH 



AND THE PRIMATES. 



1. 

 ONTOGENETIC DEVELOPMENT OF THE TEETH. 



[Reprinted from a paper in the Anatomisch.es Anzeiger, Jahrg. VII. (1892), 8vo, Jena, 

 pp. 740-747, entitled "The History and Homologies of the Human Molar Cusps 

 (a review of the contributions of Dr. A. Fleischmann, Dr. Julius Taeker, and 

 Dr. Carl Rose)".] 



THE embryonic development of the cusps of the molar teeth in the 

 Mammalia has lately been discussed in two very interesting papers by 

 Taeker 1 and Rose, 2 and the homologies of the upper and lower cusps have 

 been investigated by Fleischmann. 3 The work of the latter is based upon 

 the comparative study of recent types of molars, and the author reaches 

 the conclusion that the system of homologies proposed by Cope 4 and 

 expanded by Osborn 5 between the upper and lower molars is erroneous. 



Taeker's paper is chiefly devoted to the study of the succession and 

 embryonic form of the molar cusps in different Ungulates : he supports 

 by ontogeny the view based upon palaeontology that the ancestral cusps 

 were conical ; he shows that in the lower molars the ontogenetic order of 

 development corresponds with the phylogenetic order as traced by Cope 

 iimong the fossil forms, but that in the upper molars the ontogenetic order 

 does not correspond with the primitive phylogenetic succession as traced 



1 " Zur Kenutnis der Odontogenese bei Ungtilaten," Dorpat, 1892. 



2 " Uber die Entstehung und Formabanderungen der menschlichen Molaren," Anat. 

 Anz., 1892, Nr. 13 u. 14. 



3 " Die Grundform der Backzahne bei Saugetieren und die Homologie der einzelnen 

 Hocker," Berlin, 1891. 



4 "The mechanical Causes of the Development of the Hard Parts of the Mammalia," 

 Journ. of Morphology, 1889. Also earlier papers. 



""'The Structure and Classification of the Mesozoic Mammalia," Journ. Acud. Nat. 

 Sc. Phila., 1888, p. 240; also: "The Evolution of Mammalian Molars to and from the 

 Tritubercular Type," American Naturalist, 1888. 



