25 



ities. The trapeziumis sraall and posterior; the trapezoides has an almost 

 entirely lateral presentation, and is also small, and fits an angle of the 

 magnum ; the metacarpal facets of the latter bones are continuous and 

 uninterrupted. The magnum is flat and transverse ; the ^mcif arm is near- 

 ly as broad and less depressed ; it presents two inferior articular faces, 

 the lesser and interior for the third metacarpal ; that for the tilth meta- 

 carpal is wanting. 



There are two principal and two rudimental metacarpals. The third 

 articulates with half of the trapezoides, the magnum, and a fourth of 

 the unciform ; the fourth witb the remainder of the unciform. The 

 second and fifth are very short and wedge-shaped, and closely adherent 

 in shallow fossae of the third and fifth respectively. The latter are dis- 

 tinct, and present no traces of present or prospective attachment ; their 

 opposed faces are only flattened on the jjroximal three-fourths, and 

 rounded on the remaining fourth. Their articular extremities present 

 no basal ridge, and the median keel is i^osterior, terminating at the dis- 

 tal center. The basal phalanges are short, and with a distal trochlear 

 groove ; those of the second series are half as long. 



Measurements. 



[M. 



Length of the continuous six molars 0.058 



Depth of mandible at M. 2 022 



Length of atlas, (on centrum) 035 



Length of third cervical vertebra 056 



Width of centrum behind 020 



Depth of centrum behind 015 



Depth of centrum behind with hypapophysis 020 



Expanse of diapophyses of fourth cervical 034 



Expanse of zygapophyses of fourth cervical 038 



Length of centrum first dorsal 025 



Width of centrum first dorsal 020 



Depth of centrum first dorsal 014 



Width of humerus distally 024 



Length of radius 183 



Width of do. proximally 018 



Width of do. distally (greatest with ulna) .023 



Length of lunar, (anterior face) . .009 



Length of magnum, (anterior face) 004 



Width of carpus distally 020 



Width of III and IV metacarpals proximally 019 



Width of III metacarpal proximally Oil 



Width of III metacarpal distally . . .' 009 



Length of III metacarpal 131 



Length of proximal phalange 017 



Length of phalange of second row 010 



The above analysis determines some interesting relations of this ge- 

 nus. The cervical vertebrse indicate affinity to the Camelidce and there 

 is nothing in the remainder of the structure to contradict such relation. 

 The separation of the os trapezoides is found in the camels and very few 

 others only among Ruminantia, but in the presence of the trapezium 

 Poebrotherium shows relationships to more ancienttypes as Anoplotherii- 

 dce, &c. The reduction of the digits to two, and the separation of the 

 metacarpals point in the same direction ; indeed the number of carpals 

 and metacarpals is precisely as in Xiphodoti. But the mutual relations 

 3 & B 



