DAKOTA AND NEBRASKA. 305 



between the position of the nasals and the infra-orbital foramen. A similar but 

 deeper fossa is represented as occupying the side of the maxillary bone in advance of 

 the position of the lachr3fmal, in Hipparion gracile* 



The facial surface of the lachrymal bone is of more uiiiform width, and proportion- 

 ately narrower than in the Horse. The maxillo-malar suture preserves an oblique 

 course backward from the lachrymal, instead of a vertical one as in the latter animal. 



The infra-orbital foramen occupies a position about half an inch above the middle 

 of the third molar tooth, and about an inch from the orbit. A smaller foramen, 

 apparently an oifshoot from the former, is situated below it, in all the specimens 

 under observation. 



The fore part of the face is destroyed in all the specimens under consideration. 

 The upper part of the face has the same form as in the Horse, as is also the case with 

 the back part of the nasals and their mode of articulation with the frontals, lachry- 

 mals and maxillaries. 



The back part of the hard palate is projDortionately wider and more arched than in 

 the Horse, but otherwise has the same form. The interpalatine notch likewise has 

 the same shape, but is more narrowed posteriorly between the pterygoids. It reaches 

 as far forward as the middle of the antepenultimate molars. The palate plates of the 

 palatines have a greater proportionate width fore and aft than in the Horse. 



The lower jaw, as in the case of the upper, is of much less proportionate depth 

 than in the Horse, in accordance with the less development of the alveoli. The back 

 portion of the jaw is of less proportionate depth in comparison with its breadth, but 

 is greater in relation with the length of the whole jaw. 



The body of the lower jaw is of more uniform depth than in the Horse, and is 

 more convex and less vertical at the outer side. The posterior convex border is 

 rather abruptly prominent about an inch below the condyle. The base is slightly 

 flexuose in its course. 



The coronoid process is more curved than in the Horse, and the maxillary de- 

 pression below is deeper and better defined. The condyle and notch in advance are 

 the same as in the latter animal. 



The mental foramen appears to be irregular in character. In two specimens there 

 are several small ones extending in a row along the fore part of the jaw, varying in 

 each specimen and on the two sides. 



The end of the lower jaw in advance of the molars tapers much in the same 

 manner as in the Horse. The hiatus in advance of the teeth has an acute edge, and 

 the symphysis extends nearly as far back as the commencement of the molar series. 



The dentition of AnchWierium is expressed by the following foi'mula : 



*,AbhaadI. d. K. Bayerisch. Akad. d. Wissens. Band V, Tab.ix. 



39 



