EVOLUTION OF THE SKULL AND DENTITION OF OLIGOCENE TITANOTHERES 



569 



Measurements of Brontotherium gigas 



Millimeters 



Symphysis to angle 620 



Symphysis to condyle 600 



Depth of jaw, condyle to bottom of angle 305 



Depth of jaw below first molar 105 



Molar-premolar series 365 



True molar series 258 



Premolar series 117 



Ml, transverse 37 



Ml, anteroposterior 59 



M2, transverse 41 



M2, anteroposterior 78 



Ms, transverse 47 



Ms, anteroposterior 118 



Canine enamel, anterior 34 



Canine, anteroposterior 30 



Length of symphysis 173 



the fourth premolar and then ascends rapidly to the 

 incisive border with a slightly convex chin, but there 

 is an interval between the chin and the canine that is 

 concave and somewhat hollowed out beneath. The coro- 



FiGURB 471. — Lower jaws of Brontotherium gigas and B. medium 

 A, Brontotherium gigas, Yale Mus. 12061 (type of Tiianops elatus). This animal has the measurement of mi-ma longer than in the type 

 of is. gigas and may represent a slightly higher stage. The angle is very prominent and rugose, as in old animals. The molars have 

 reduced external cingula. B, B. medium, Am. Mus. 1051; the largest known titanothere jaw. It conforms in all important respects to 

 the Brontotherium type. One-fifth natural size. , 



The jaw is of the true bronto there type. The men- 

 tal foramen is at a point vertically below the posterior 

 fang of the third premolar. Above and behind it are 

 two smaller foramina. The jaw is swollen beneath 



nary process as figured is restored at the tip ; the ante- 

 rior border presents a smooth, rounded ridge antero- 

 externally, which is brought into further prominence 

 by a depression running just back of and parallel with it. 



