No. 377-] THE ORIGIN OF THE MAMMALIA. 315 
has recently been thrown in doubt by Woodward). The hypothe- 
sis as to the derivation of the multitubercular from the trituber- 
cular teeth was based upon the fact that certain rodents, although 
unquestionably of trituberculate origin, present typical multi- 
tuberculate teeth. Summing up as follows: The Lower Triassic 
ancestors of monotremes, marsupials, and placentals possessed 
teeth differentiating into different kinds (inctptently heterodont), 
molars with three cones (triconodont) and dividing fangs (Proto- 
Parietal 
of the cranial 
Fic. 2. — Lateral view of the skull of Dicynod 
elements. (After Seeley.) 
donta), giving rise both to the multituberculate and trituberculate 
types, with the dental formula: incisors, 4; canines, I; premolars, 
4 or 5; molars, 8. 
These assumptions are in a measure confirmed by Professor 
Seeley’s discoveries, but the Theromora in the large sense 
reassume a position ancestral to rather than parallel with the 
mammals. Before bringing out all the grounds for this state- 
ment let us review the osteological and dental promammal 
characters side by side with theriodont characters. 
II. History OF DISCOVERY. 
Professor Owen defined the Theriodontia in 1876 as follows: 
“Dentition of a carnivorous type; incisors defined by 
position, and divided from molars by a large laniari- 
form canine on each side of both upper and lower jaws, 
the lower canine crossing in front of the upper; no 
