MERYCOIDODON 49 



in part, and the masseteric fossa is large. The condyle is inset well forward from the posterior edge 

 of the ramus, and the sigmoid notch is shallow and wide open. The coronoid process is short and 

 thin. 



Foramina: The infraorbitals usually lie above the interval between P 2 and P 3 , although they 

 may be placed as far aft as over the middle of P 3 . The supraorbitals are close to the sagittal suture 

 and are generally not more than 10 mm. apart. The large foramen ovale is placed just in advance 

 of the bulla and close to the posterior termination of the sphenoid bone. The small foramen 

 rotundum lies anterointernal to the foramen ovale. The foramen lacerum anterius (sphenoidal fis- 

 sure) is very large. The posterior palatine foramina are about opposite the middle of P 4 but may be 

 slightly farther forward. 



Dentition: The teeth are brachyodont. Superior: The molars have well-developed parastyles 

 and mesostyles. The hypocones are somewhat smaller than the protocones. The paracones and 

 metacones are set at an angle to each other. The protocones have anterior and posterior cingula, as 



Fig. 22. — Merycoidodon culbertsonii Leidy. Crown view of left superior dentition. Nat. size. (Redrawn from 



Leidy, 18 5+.) 



have the hypocones, except that the latter of M 3 has an internal one as well. P 4 , in an unworn 

 tooth, possesses an anteroexternal pit, which is the only residual of the anterior part of this tooth. 

 The posterior basin is well developed in all of the anterior premolars. The anterior basin is equally 

 divided by an anterointermediate crest. The premolars are moderately broad, and the anterior part 

 is somewhat reduced, especially that of P 3 . The canine is large and robust, with a subtriangular 

 cross section. The incisors are small and have an internal cingulum. 



Inferior: The metastylid of M :! is well developed. The stylids are feebly developed. The 

 premolars are usually not crowded, though they are in some specimens. The anterior, posterior, 

 and median crests are well developed. There is no anterointermediate crest, and the posterointer- 

 mediate is weak and takes off from the median crest, instead of from the primary cusp. This is a 

 feature peculiar to these premolars. Pi is large and lenticular in section. The crowns of the 

 incisors are longer than those of the superior series. 



The molar-premolar index of the superior series is 0.84 to 1.00 and that of the inferior 0.88 

 to 0.89. 



Skeleton: The hyoid bones are rarely found in fossil skeletons, but one individual of this 

 species, collected on Warbonnet Creek, Sioux County, Nebraska, has them excellently preserved. It 

 is Cat. No. 12239 Y.P.M. 



The stylohyoid is the largest of these bones. Its direction was downward, slightly forward, 

 and somewhat inward, being connected with the skull between the small auditory bulla and the 

 postglenoid process, with its cartilaginous attachment having its origin probably near the stylomas- 

 toid foramen. This bone is strongly compressed laterally, with the dorsal border slightly thicker 

 than the ventral. Both ends are vertically enlarged, with the result that the anterior (dorsal) side 

 is concave forward and the opposite side concave backward, leaving a constriction about midway of 

 the bone. The muscular angle of this great cornu is well developed, and the lower end is enlarged. 



