68 
ptychodont, bunodont and lophodont teeth, (tlie two last mentioned 
belonging especially to the Ungulates) and he showed how the 
lophodont teeth can be derived from the bunodont by further devel- 
opment of the various cusps, a development which is accompanied 
by the palæontological development of the foot. 
1878 Ryder tried to explain the tooth-structure from modern 
ideas of “evolutional teleology”. The tooth-form according to him 
depends, not only on the nature of the food, but also on the mo\e- 
ment of the lower jaw, and this acts also on the form of the con- 
dvle. The earliest and simplest type of mammalian jaw-movement 
was that in which the mouth was simply opened and closed, without 
mandibular excursion, and coexistent with the simple haplodont or 
bunodont molar.“ (pag. 79). „As the excursive movements have 
increased in complexity, there has been an apparent increase in the 
complexity of the enamel foldings, ridges and crests.“ (pag. 80). 
And the differentiations are due to a „necessary, voluntary or in¬ 
telligent assumption“ of new life-habits (pag. 53). The various 
tooth-forms are produced by duplication of cusps in various diiec- 
tions, fusion, suppression, enlargement etc. „These [differentiations] . . . 
make further differentiations, which are successively fixed by the law 
of heredity, less difficult in succeding generations, until extremes 
are reached“. (pag. 70). 
In the same year Gaudry declared that the complicated molars 
of the Ruminantia were formed by fusion of several more simple 
teeth, the upper made up of 6, the lower of 4 or 2. This is the 
lirst appearance of the “Concrescence Theory”. 
In his book “Odontologische Forschungen” 1882 Baume set 
fortk many new thoughts, which, however, are often more original 
than convincing. He thought he had found a „Thatsache von 
hochster Wichtigkeit“: „Das Gebiss der Vertebraten befindet sich 
in steter Reduction, was die Zahl der Zåhne und die Masse der 
Zahnsubstanzen anbetrifft. Es herrscht ein ganz bestimmtes Gesetz, 
welches ich das Gesetz der Reduction nenne. Das Gesetz dei 
Reduction erklårt alle Abiinderungen im Gebiss.“ (pag. 78). The 
