No. 2.] THE RELATIONS OF PROTOCERAS. 313 



may be quoted here with advantage. " In MoscJms the auditory 

 bulla is remarkably small, the petrous portion of the periotic be- 

 ing visible, when viewing the base of the skull, for nearly the 

 entire length of the bulla from before backwards. The tym- 

 panic is considerably prolonged to form the inferior floor of 

 the external auditory meatus " (No. i, pp. 522-3). In Proto- 

 ceras the approximation of the tympanic and basioccipital is 

 too close to allow the periotic to be seen, except in one speci- 

 men where the exposure is clearly due to a displacement of the 

 surrounding parts. As in Leptomeryx and in the Pecora gener- 

 ally, the tympanic is hollow and not filled with cancellous 

 tissue, but the bulla of Leptomeryx, though decidedly smaller 

 than in Tragnlus, is relatively much larger than in Protoceras. 

 The mastoid portion of the periotic forms a narrow and more 

 or less rugose strip between the exoccipital and the squamosal, 

 and is continued upon the anterior face of the paroccipital 

 process for some distance below the posttympanic. 



The squamosal forms a varying part of the side wall of the 

 cranium, the ascending plate rising higher in some specimens 

 than in others. The parietal suture is regularly arched upward 

 and backward. As in the deer, the bone forms a truncated 

 process at the anterior end of this suture, where the cranial 

 wall turns inward to form the front boundary of the cerebral 

 fossa ; apparently, however, the alisphenoid takes less share in 

 the formation of this process than is the case in Cervics. The 

 root of the zygomatic process is thicker and less concave on its 

 upper side than in the recent Pecora and the process itself is 

 heavier than in those animals, in which it is remarkably weak ; 

 as to length, it is longer than in the cavicorns and shorter than 

 in the deer, the orbit occupying a position intermediate be- 

 tween the rather anterior place it holds in the latter, espe- 

 cially in the hornless forms, and its very posterior position 

 in the former. The glenoid cavity is typically ruminant in 

 character ; in front it is broad and slightly convex, passing 

 behind into a concavity. The postglenoid process is longer 

 and considerably heavier than in most recent ruminants, 

 though very much less so than in such types as the oreodonts 

 or Ancodiis. The process does not, as in the deer, bound the 



