Ti;rrrr,Ki:<n.Y ix I-KI.MATKS 49 



by Cope. Upon the whole, however, he finds a very striking parallelism 1 

 between embryogeny and phylogeny both as to the form and succession of 

 the cusps (see Table mi p. Til ). 



Rose's paper is also of great value in proving that in Homo and 

 It'idc/jilii/*, representing two widely separate classes, the embryonic history 

 of the lower molars approximately repeats the ancestral history: he 

 independently supports Taeker in the conclusion that the upper molar 

 cusps do not repeat the ancestral order assigned by the Cope-Osborn 

 theory, he therefore agrees with Fleischmann that we have mistaken the 

 history and homologies of the upper molar cusps, and suggests very 

 courteously that the Osborn nomenclature should be transposed to cor- 

 respond with the embryological order ; he further advances the original 

 theory that the mammalian cusps have arisen not by addition to the 

 single reptilian cone, but by the fusion of a number of cones together. I 

 will first consider the main principles involved in these papers, and then 

 mention some of the less important special points. The following table 

 exhibits the correspondence and contrast between the phyletic and 

 embryonic succession, as well as the homologies and order of appearance, 

 according to the Cope-Osborn theory. 



From this table the striking parallelism between ontogeny and 

 phylogeny in the lower molars is brought out. Also the contrast between 

 the early appearance of the hypoconid both in phylogeny and ontogeny 

 and the late appearance of the Jn/pocone phylogenetically and ontogeneti- 

 cally, 



1. That iJie primitive form of mammalian molar was a siiif/le cone to 

 which all the other cusps have been successively added. I may first take 

 up the different theory of cusp origin proposed by Rose, and observe that 

 whatever support it may receive from embryology is offset by the over- 

 whelming evidence of palaeontology. In figure 38. I have epitomized the 

 slow transformation of the single-fanged conical reptilian tooth (1), such 

 as we see persisting in the Cetacea,* into the low-crowned human lower 

 molar (8). The first departure towards the development of lateral cusps 

 is seen in the triassic Dromatherium (2) ; the second is in the contem- 

 porary Micron i, iddini (3) : the third is in the Jurassic Spalacofhcri/nn (4) ; 

 in the fourth (Amphitli&rium, Jurassic) (5), we see the three cusps of the 

 primitive triangle and the first cusp of the talon, hi/' 1 . In Miacis of the 

 lower Eocene (6) the figures of the internal and crown views of the three 

 molars show how the primitive anterior portion (trigonid) of the crown 

 was reduced to the level of the posterior portion (talonid) while retaining 

 all of its cusps. In the next figure (7) we see the lower molars of the 



1 See Osborn, " Odontogenesis in the Ungulates," A met: Aat., 1892, p. 621. A fuller 

 review of Dr. Taeker's paper. 



*[More probably secondary in Cetacea. See pp. 79, 190. Ei>.] 



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