1896. ] MAMMALIAN DENTITION. 585 
cusp phylogeny as advanced by the supporters of the Cope-Osborn 
tritubercular theory. This is a very striking and important fact, 
and one which will no doubt be considered by trituberculists as 
strongly supporting their theory, especially as it is generally stated 
that these trituberculate Insectivores most nearly, amongst living 
mammals, approach the Jurassic Trituberculata in the character 
of their molars. This statement is certainly true for the lower jaw, 
but can be hardly said to hold for the upper molars, there being no 
resemblance between the teeth of the upper jaw of Centetes, Hriculus, 
and. Chrysochloris * and those of Peralestes, and only an apparent one 
with Kurtodon (Stylodon), for Osborn (16) himself states that this 
latter is not trituberculate but ridged *. 
Turning now to the first group and examining it in the light of 
the supposed primitive nature of the protocone, we find here that 
the upper molar teeth are more complex, possessing 4 or 5 cusps, 
that the outer cusps (the para- and meta-cones) are more strongly 
developed than the inner ones; and in accordance with this we find 
both these cusps developing before the protocone—an anomalous 
condition when we remember that the last-named cusp is sup- 
posed to be the primitive axis of the tooth, the remaining cusps 
being mere outgrowths from it. Perhaps, if these Insectivora 
were the only forms possessed of such a condition, we might agree 
with Osborn (15) that this is merely a case of accelerated 
development ; but they are not alone in this respect, for in Man 
(19), in some Ungulates (22), and in certain polyprotodont 
Marsupials (20), the paracone invariably develops first, the 
protocone being either 2nd or 3rdin order of appearance. In fact, 
in every mammal so far examined, with the exception of the two 
Insectivores before mentioned, the paracone develops directly from 
the primitive dental germ and before either the protocone or meta- 
cone. The constancy of this condition is such that I do not think we 
can pass over it so lightly as Osborn does, as may be seen from the 
following quotation (15. p. 503): “In fact the external cusps not 
only appear before the internal cusp, which paleontology shows to 
be the more primitive, but they assume the crescentic form earlier, 
In other words, their development is accelerated.” (Italics mine.) 
If the protocone represents the summit of the original protodont 
tooth of the ancestor of the Mammalia, it must be the direct con- 
tinuation of the primitive dentinal germ, and as such should be found 
to develop in a line with the axis of that.structure. That this is not 
the case is well seen in fig. 32 (Pl. XXVL.), where the paracone (5) 
is found to be identical with the primitive dentinal germ and the 
protocone (7) appears as a mere internal ledge growing out from 
* Chrysochloris is trituberculo-sectorial, possessing a small heel, and not a 
pure trituberculate as usually stated. ILydekker (10) compares Peralestes and 
Chrysochloris, but I fail to see the resemblance. 
* It is very difficult to ascertain Osborn’s views regarding Kurtodon, for in 
his large memoir (16. p. 210) he states that there is no real homology between 
the Kurtodon and Chrysochloris dentition, whereas in his additional notes ( 16 ¢) 
he appears to regard Kurtodon as one of the Trituberculata. 
Proc. Zoot. Soc.—1896, No. XX XVIII. 38 
