1913] 



Merriam: Horses of Rancho La Brea 



409 



In the lower milk molars (fig. 14), the outer fold between 

 the protoeonid and hypoconid pushes farther in toward the 

 middle of the tooth than in the permanent premolars. The 

 small fold or jog on the posterior side of this outer fold is well 

 marked. The small fold on the antero-external angle of Dm 4 is 

 well shown. 



Figs. 12 and 13. Equus occidentalis Leidy. Superior milk dentition, 

 no. 20099, X %. Ranclio La Brea Beds, California. Fig. 12, temporary 

 incisors; fig. 13, temporary molars. 



Fig. 14. Equus occidentalis Leidy. Inferior temporary molars, no. 

 21072, X y 2 . Rancho La Brea Beds, California. 



Measurements of all cheek-teeth are made exclusive of the cement. 



In the upper dentition, excepting in P~ and Ms, the anteroposterior 

 diameter is measured along the middle of each tooth, between the principal 

 anterior and posterior faces of contact with the adjoining teeth. In P- 

 and M3 the anteroposterior diameter is measured from the middle of the 

 face of contact with the adjoining tooth to the extreme opposite limit of 

 the tooth. In P3 to M 2 the anteroposterior diameter does not include the 

 anterior projection of the parastyle in advance of the principal anterior 

 contact plane of the tooth. Transverse diameters are measured across 

 from mesostyle to the innermost extent of the protocone. 



In the lower cheek-teeth the anteroposterior diameter is measured as in 

 the superior series, and includes the limits measured along the middle of 

 the tooth. The transverse diameter of the lower cheek-teeth is the greatest 

 diameter measured across the protoeonid and metaconid excepting in P 2 . 

 In P 2 the transverse measurement is across hypoconid and entoconid. 



14 



Measurements of Dentition 



