No. 3.] OSTEOLOGY OF MESOHIPPUS AND LEPTOMERYX. 3 5 I 



a broad, much depressed, and opisthoccelous centrum ; the con- 

 dyles for the atlas rise higher upon the sides of the neural canal 

 than in the modern genus. The odontoid process is short and 

 peg-shaped, not in the least like the spout which occurs among 

 the true ruminants. In the Cope collection, however, there is 

 a small axis with a broad depressed odontoid, much as in Oreodon, 

 but this may belong to Hypisodus. The transverse processes 

 of the axis are short and slender and perforated by the verte- 

 brarterial canal. The neural spine is developed into a great 

 hatchet-shaped plate ; the upper margin of this spine is nearly 

 straight and the posterior edge almost vertical, while the anterior 

 one curves gently downward and forward. In spite of its great 

 size, the spine overhangs the third vertebra hardly at all. This 

 spine differs strongly from the corresponding ones of Cainothe- 

 rinm and Tragalus. The third cervical has a rather long 

 opisthocoelous centrum with a slight keel ; the spine is a low 

 ridge. The fourth vertebra is somewhat shorter than the third, 

 but has a more distinct keel, ending posteriorly in a stout 

 tubercle ; the neural spine is short, slender, and inclined dis- 

 tinctly forward. The fifth vertebra is like the fourth, except 

 that it has no keel on the centrum and that the neural spine is 

 considerably higher. On the sixth the spine is still higher, 

 much better developed, indeed, than in Tragulns, and as in 

 that genus, the transverse process has a large pleurapophysial 

 plate. The seventh cervical is decidedly the shortest vertebra 

 of the series, but has the same depressed, opisthoccelous shape 

 as the others ; the spine is very much stouter than that of 

 the preceding vertebras and much heavier than in the modern 

 genus. 



The anterior dorsals are very small ; they have short and 

 simple transverse processes, terminating in concave facets for the 

 tubercles of the ribs. The spines are proportionately stouter 

 than in Tragulus, and incline strongly backward. 



The lumbar vertebrae are relatively shorter than in the tragu- 

 lines and indicate a less strongly arched back, which is also 

 borne out by the fact that the disproportion between the length 

 of the fore and hind limbs is not so great as in Tragulus. 



The rib fragments which are preserved indicate a thorax simi- 

 lar to that of the modern genus. Nothing is known of the 

 sternum. 



