No. i.] OSTEOLOGY OF PCEBROTHERIUM. 2$ 



and posterior portions, but the former has not attained any such 

 development as appears in the camel. The neural arch is low 

 in front and rises behind, and the pedicels are deeply notched 

 anteriorly for the passage of the spinal nerves. The neural 

 spine is represented only by a very feebly marked ridge. The 

 postzygapophyses are much larger and diverge much more 

 strongly than the prezygapophyses, and from the base of the 

 latter a sharp ridge runs posteriorly along the side of the pedi- 

 cel of the neural arch. There is in this vertebra no visible 

 opening for the vertebrarterial canal. 



The fourth cervical is slightly shorter than the third, measur- 

 ing about six-sevenths of its length, but is otherwise very much 

 like it. The anterior portion of the transverse process is, how- 

 ever, more developed, and more clearly distinguished from the 

 posterior portion, and projects downward, somewhat as in the 

 recent forms, but to a much less marked degree. The infe- 

 rior keel and tubercle are more prominent than on the third 

 vertebra. 



The fifth cervical is shorter than the fourth, about five- 

 sevenths of its length, but differs from it in no other important 

 respect, except that the separation of the transverse process 

 into anterior and posterior portions is more distinct. On both 

 of these vertebras the down-projecting anterior portion of the 

 transverse process is very different in shape from that which 

 occurs in the recent genera, being much less massive and 

 rugose, and having thickened and regularly curved margins, 

 which extend somewhat in advance of the anterior face of the 

 centrum. Neither this vertebra nor its predecessor has a 

 neural spine or visible vertebrarterial canal. 



The sixth cervical is strikingly different from the others, and 

 is less like its representative in the modern genera than any 

 other vertebra of the neck. The centrum is considerably 

 shorter than that of the fifth vertebra, which, in the specimen 

 we are describing, measures 56 mm. in length, while the sixth 

 measures but 45 mm., and is higher in proportion to its breadth. 

 The anterior face is quite strongly convex and nearly hemi- 

 spherical in shape, the posterior as strongly concave. The 

 inferior keel and tubercle are almost obsolete. The neural 

 arch is high and is occupied throughout its length by a thick 

 neural spine, which is unfortunately broken away in the only 



