88 THE MAMMALIA OF THE DEEP BIVER BEDS. 



assistant, Mr. Graham, and on further examination I find it to be frequently the case 

 in other phyla, that the breadth of this border and the depth of the groove diminish 

 in the more modernized forms. 



The radius has a slender, flattened shaft, which expands distally and is also 

 much thickened antero-posteriorly, so as to be of trihedral section. In this respect, 

 Desmaiippus resembles the less advanced genera and differs in a marked way from 

 ProtoMppus and the later forms. The distal thickening is entirely on the anterior 

 face, the posterior side remaining flat or even slightly concave. The distal ends of 

 the radius and ulna are firmly coossified for a length of about two inches ; above 

 this, the shaft of the radius has upon its postero-external edge a shallow and narrow 

 groove for the shaft of the ulna, which was obviously very slender, though probably 

 not interrupted. The carpal surfaces of the forearm bones are too much mutilated 

 for description. 



Of the metacarpals, the third is preserved entire and also portions of the second. 

 The former is remarkable for its slenderness and length, in which latter respect it 

 considerably exceeds that of ProtoMppus sejunctus. Unfortunately, the proximal 

 articular surfaces are so much broken that they cannot be made out satisfactorily. 

 The distal end exhibits some important features which are intermediate between the 

 more ancient and the later genera. As in the former, the shaft is expanded trans- 

 versely just above the trochlea, which is narrower, while in JEJquus the trochlea is 

 wider than any portion of the shaft. As compared with the earlier forms, the troch- 

 lea is higher and the carina, which in all preceding genera is confined to the palmar 

 side, is in Desmaiippus continued over the entire anterior face of the articular sur- 

 face; very faintly, it is true, and yet unmistakably. This genus is therefore the 

 first, at least in the direct line of descent, in which this characteristic equine feature 

 appears. 



The character of the phalanges will be best explained after quoting Kowalevsky's 

 comparison between those of AnchiJierium and Equus : " Par la forme des phalanges 

 l'Anchitherium diftere completement du cheval et de l'hipparion ; il lui manque ce 

 retrecissement si considerable qui est characteristique pour la premiere phalange des 

 equides ; les phalanges du Daw qui out 09 mm. de long, presentent au milieu une 

 largeur transverse de 25 mm., tandis que les phalanges de l'Anchitherium qui n'ont 

 que 35 mm. de longueur, e'est-a-dire la moitie, presentent au milieu une largeur trans- 

 verse plus considerable, 20 mm." (JSTo. 20, p. 60). 



In Desmaiippus the proximal phalanx of the median digit has already attained 

 proportions which closely approximate those seen in JEquus. The relative breadth 

 of the proximal and distal ends is almost the same as in the horse, but the contrac- 



