85 
condition to a transverse one and a constant development of certain 
cusps with fusion and suppression of others, the different later molar 
types were formed. Which of the cusps may be homologous with 
the "reptilian cone” is not known. 
The same year an important corrective to the Osborn theory 
was advanced by Scott ("Evolution of the Premolar Teeth”). He 
asserts that the evolution of the premolars is not the same as that 
of the molars. Sometimes even på is found as a single conical 
tooth, evidently corresponding to the protocone of the molars. But 
already in the Puerco beds a little protuberance, the deuterocone, 
appears on the lingual side of pt, thereafter a third cusp, the 
tfritocone, appears behind the protocone; now the tooth closely 
resembles the trigonodont molar, but the protocone still occupies 
its place on .the outer side of the tooth. Finally a tetartocone 
may originate behind the deuterocone so that the tooth becomes 
quadrituberculate, of the same shapeas the quadrituberculate molar, 
although the cusps are of different origin. pt is often fully devel- 
oped, whereas the foremost premolars still preserve a very primitive 
shape. — The development of the lower premolars is also different 
from that of the molars; the protoconid certainly keeps its place on the 
Outer side of the tooth, but no rotation of the para- and metaconid 
OCcurs, so that the metaconid becomes an element of the talonid ; 
the tooth finally becomes quinque-tubercular like the molar. The 
Cusps of upper and lower premolars and molars correspond thus 
With one another: 
Upper jaw. Lower jaw. 
Premolar Molar Premolar |. Molar 
Deuterocone | Protocone Protoconid | Protoconid 
Protocone ”Paracone Paraconid | ”Paraconid 
Tritocone — | Metacone =— — — Deuteroconid  Metaconid 
Tetartocone ; ”Hypocone Metaconid Hypoconid 
DN HE fo RE Tetartoconid Entoconid 
This evolution can be traced through most of the mammalian orders. 
