280 DR. H. W. MARETT TIMS ON 
Of the various theories which have been propounded to account 
for the origin of the complex crown of the Mammalian molars 
from the Haplodont type, it will be necessary to refer to three 
only. They are the Tritubercular, the Multitubercular, both of 
which are well known, and the theory of Cingulum-Cusp 
development suggested by me in my work on the Canide. 
Tritubercular Theory.—This view,so ably advocated by Cope 
and Osborn in America, and so widely accepted both in this: 
country and on the continent, is too well known to need any 
re-statement. One of the important arguments advanced against 
this theory is that the Paracone, and not the Protocone, is 
ontogenetically the first to appear. This has been found to be 
the case in Marsupials [15], Carnivores [22], Ungulates [20], 
some Insectivores [28], and Primates [16 and17]. To these 
may now be added Cavia, as representing the Rodents. The other 
cusps are secondarily added. 
The Multitubercular Theory, first put forward by Forsyth 
Major, suggests the primitive condition of the mammalian 
cheek-teeth to have been multituberculate, and that during the 
course of evolution a diminution in the number of cusps has 
taken place. This theory does not appear to me to be applicable 
to such Orders as those just mentioned with their full complement 
of teeth, and in which embryology has shown that the teeth 
develope by the addition of cusps to a single primitive cone.. 
It is evident that this theory presupposes the acceptance of the 
Concrescence theory as set forth by Dybowski, Gervais, Rose, 
and more particularly by Kikenthal. Though I am unable to 
accept these combined views as a whole to account for the origin 
of the Rodent molars, nevertheless they afford a certain amount 
of satisfactory evidence; the suggestion which I would offer 
will be discussed subsequently. 
Theory of Cingulum-Cusp development.—The uniformity of 
development of the antero-external cones in both jaws suggests the 
Paracone and Protoconid as being homologous, and as representing 
the primitive reptilian cones. The remaining cusps I believe to 
have been mainly derived from the Cingulum, a structure of great 
antiquity as shown both embryologically and paleontologically. 
The details of the subsequent development of the cusps I need 
not here repeat, as they have been already published [22]. This 
view is in harmony with the Tritubercular theory up to the 
