No. 2.] THE RELATIONS OF PROTOCERAS. 329 



and, as the vertebral artery " usually enters the neural canal 

 between the arches of the second and third vertebras," the 

 transverse process is generally not perforated by the verte- 

 brarterial canal, but is pierced anteriorly by the inferior branch 

 of the second spinal nerve. In Protoceras, on the other hand, 

 the pedicel is imperforate, the nerve passing out through the 

 deep notch which separates the atlanteal facet from the neural 

 arch. As the transverse process arises behind this point, it 

 does not traverse the path of the inferior branch of the nerve, 

 and hence there is no foramen for that branch. The process 

 is perforated, however, by the vertebrarterial canal, both open- 

 ings of which are present, and the artery probably entered the 

 neural canal between the arches of the atlas and axis. 



None of the specimens contain representatives of the third 

 or fourth vertebra. 



The fifth cervical is relatively short, both actually and pro- 

 portionately shorter than in Mosc/ms, an animal which agrees 

 well with this species in stature. The centrum is of depressed 

 cylindrical shape, is strongly opisthocoelous and the faces 

 are markedly oblique to the long axis of the vertebra. On the 

 ventral surface is a prominent, but very thin and fragile keel, 

 which terminates posteriorly in a hypapophysial tubercle. The 

 neural arch is broad and nearly plane on the dorsal side and 

 carries a spine which is much higher than in Moschus and 

 which tapers and rapidly becomes very slender, though its base 

 occupies nearly the whole length of the neural arch. The 

 zygapophyses are large and widely separated on the two sides ; 

 the anterior pair are the narrower and present obliquely inward 

 as well as upward. As the obliquity of the centrum is more 

 decided than that of the neural arch, the pedicels of the arch 

 are very low in front, and hence the ventral sides of the pre- 

 zygapophyses are separated from the centrum only by narrow 

 notches. The postzygapophyses are larger and more promi- 

 nent than the anterior pair and project directly downward, 

 almost without obliquity. The neural canal is broad and low, 

 especially in front ; posteriorly the increased height of the 

 pedicels and obliquity of the centrum give it greater height. 

 The transverse process is so mutilated on both sides that its 



