1900.] STRUCTURE OF THE MUSK-OX. 713 



column. It is also very easy to understand how the short basal 

 tubercles in primitive forms, with comparatively short teeth, for 

 this reason are transformed to columns in higher, more specialized, 

 forms with long teeth. At the same time that the teeth are 

 developed from brachydont to hypselodont, the basal or accessory 

 elements are drawn out in length. The " Basalwulst " does not 

 exist any longer in the hypselodont teeth. The formerly basal 

 elements must therefore take their origin at the vertical surface of 

 one of the main lobes, and become easily soldered to them, as is 

 the case in the mandibular molars of the Bovinse. In this way 

 the short basal tubercles are gradually changed into long columns, 

 which together with the teeth themselves may become enlarged 

 and add to the grinding-power of the teeth. Under such cir- 

 cumstances it should be only their situation at the inner side 

 of the upper true molars that should guarantee to the accessory 

 elements of these teeth the rank of " accessory columns," 1 and 

 something different from the common " basal tubercles." This is, 

 however, far from sure. Biititneyer regards the, as he thinks, true 

 accessory columns as " Abgliederungen vom Vorjoch dieser Zahne " 

 (Anoplotherium molars). In the young, not yet fully developed, 

 first molars of the common calf I have seen the beginning of the 

 accessory columns connected with the posterior lobes. Zittel 3 

 thinks that Anoplotherince have become extinct without leaving any 

 progeny. Dichobunince, on the contrary, characterized by the same 

 author as having " Obere M. fiinfhockerig, die Zwischenhbcker in 

 der hinteren Beihe," are regarded as ancestors of the now existing 

 ruminants 3 . The latter opinion agrees consequently better with 

 the condition found in the common calf. But it is not so with 

 all ruminants : in Cephalophus, for instance, the accessory elements 

 of some of the upper true molars belong very plainly to the 

 auterior lobes, and the same is the case with all Ovibos molars. It 

 is thus apparent that the place of origin of these accessory elements 

 of the upper molars varies a good deal, and consequently cannot in 

 any higher degree be taken into accouut for systematic purposes. 

 It may also justly be questioned whether the " true " accessory 

 columns are to be regarded as " Abgliederungen " from the primary 

 lobes of the teeth ; and, if they should be so, what are then the 

 common basal tubercles ? I do not hesitate to express the opinion 

 that both the accessory columns and the basal tubercles have a 

 similar origin, namely, are more or less developed basal tubercles 4 . 



1 But in some instances not even this is sufficient, since Riitimeyer means 

 that the accessory elements on the inner side of the molars in the Giraffe and 

 the Deer ought to be regarded as " Basalwarzen " (I. c. p. 79). 



2 Handbuch d. Palaontologie, I. iy. 



3 This theory seems later to have been accepted by Rutiineyer too. 



4 A similar opinion seems also to be accepted by later authors. Rose and 

 Bartels in their paper " Ueber die Zahnentwicklung des Rindes" (Morph. Arb. 

 herausg. v. Schwalbe, Bd. 6) shortly remark (I. c. p. 97) about " die eigenartigen 

 Basalpfeiler und Faltenbildungen...welche besonders die Zahne der Rinder so 

 ausserordentlich kompliciren," that these are " ganz nachtragliche Ausstiilp- 

 ungen des Zahnbeinkeimes." 



