76 
developement of the hard parts of the Mammalia”) sets forth several 
laws for the development of the various tooth-forms, according 
to which the appearance of cusps and crests is due to a more or 
less extensive use and consequent strain in certain directions. The 
primitive tooth-form is the conical, from which at an early stage 
the triconodont arises: ,,No mechanical cause can be assigned for 
the development of these cusps, but the nutrition of the parts pro- 
bably has had an important influence on the process"; the basal 
cuspules being situated nearer the nutritive artery than are the 
remaining cuspules (Dromatherium) they will accordingly increase 
at the expense of the latter. The para- and metacone (-id) fill up 
the space between the teeth and the effective area of these is thus 
increased. The smaller cusps being least resistant to strains will 
be pushed to the outside of the row (outwards above, inwards be- 
low) whereas the median cone will retain its place. We thus get 
the tritubercular tooth which is seen in several primitive creodonts 
(Didelphodus, Stypolophus, Mioclænus) together with Chrysochloris 
and Centetes. From this type the tuberculo-sectorial dentition.is 
developed as stated by Osborn. The development of the quadri- 
tubercular tooth with its four equal cusps is due to the transition 
to vegetable diet which is not cut, but crushed, and it is accom- 
panied by the transition from the unguiculate to the ungulate foot- 
construction. — The paraconid probably decreases because the talonid 
during its growth draws the nutrition from it. — The quadritu- 
bercular teeth do not alternate like the sectorial. 
In the following years the question of the phylogeny of 
the teeth specially occupies German naturalists. 1890 Schlosser's 
"Die Differenzierung des Såugetiergebisses” appears. He finds 
the primitive tooth-form represented in the teeth of the dolphins, 
because these animals, owing to their aquatic habits, have not 
been compelled to acquire the grinding habit and therefore 
have kept their primitive character. In the terrestrial mammals 
three important things happen when they are forced to masticate 
their food: the jaws become shorter in order to utilise the muscular 
power better, the tooth-number decreases in the shorter jaw, but 
