NO. 2086. 



SOME MAMMALS OF THE PLEISTOCENE— HAY. 



567 



of the Oligocene, we shall find that the premolar series formed only 

 about 48 per cent of the length of the lower premolar-molar series, 

 omitting the minute front premolar (pmj. The present writer is 

 of the opinion that it would be difficult to prove the proposition that 

 in the horses in general the lower premolar series has become rela- 

 tively shorter in the more recent than it was in the earlier forms. 

 It would be quite as difficult to prove that the " lobus tertius " of 

 the hindermost molar has increased in length as compared with the 

 whole length of the molar mentioned. 



Soergel described and figured a quite complete lower jaw of a horse 

 which had been found at Steinheim. This author has measured the 

 height of the horizontal ramus of his specimen at seven places, as in 

 the table below, and has given the heights in hundredths of the length 

 of the lower row of cheek teeth. For purposes of comparison he has 

 done the same with three other fossil horses of his region and with a 

 specimen of the domestic horse. From his comparisons he has con- 

 cluded that the height of the lower ramus in the older forms of 

 horses was greater relatively to the tooth row than in the more recent 

 forms ; that the reduction in height from the rear forward was more 

 gradual, and that consequently in the older forms this part of the jaw 

 was heavier than in the later horses. To test the applicability of 

 these conclusions to the American Pleistocene horses the present 

 writer has prepared the following table, in which the jaws are 

 measured after Soergel's method. Soergel's measurements of E. 

 cab alius are included. The horse which furnishes the measurements 

 of the fourth column is the one in the United States National 

 Museum whose basilar length is 610 mm. 



Dimensions in jaws in hundredths of the length of the tooth line. 



Dimensions taken. 



E. nio- 

 brarensis. 



E. hatch- 

 eri. 



E. cabal- 

 lus of 

 Soergel. 



E. cabal- 

 lus, U. S. 

 Nat.Mus. 



E. cabal- 

 lus 

 Arab. 



Height behind ni3 



Height between m 3 and m 2 . . . 

 Height between ni2 and mi . . . 

 Height between mi and pm^ . 

 Height between pnu and pm3 

 Height between prri3 and pm 2 

 Height in front of pm 2 



71.2 

 57.4 

 53.0 

 52.4 

 49.1 

 44.2 

 38.0 



68.1 

 57.4 

 54.2 

 52.6 

 50.0 

 45.7 

 38.3 



59.6 

 47.6 

 44.5 

 41.5 

 37.8 

 34.7 

 26.9 



65.7 

 55.4 

 51.1 

 48.9 

 47.3 

 41.8 

 37.5 



67.2 

 53.3 

 47.8 

 45.4 

 43.0 

 39.4 

 30.3 



If now we find in each of the specimens here studied the ratio be- 

 tween the uppermost number in each case and the lowermost we shall 

 have an expression showing the amount of descent in the jaw in 

 going from the rear of the hindermost molar to the front of the 

 anterior premolar. These ratios given in order are : 53.5 for E. nio- 

 brarensis; 56.2 for E. hatcheri; 45.1 for Soergel's E. caballus; 57.1 

 for the large E. caballus; and 45.1 for the Arabian. From this it 

 appears that the large specimen of E. caballus has a lower jaw which 



