TRANSACTIONS OF WAGNER 

 28 



UINTA SELENODONTS 



size. It does not come into contact with the paroccipital process at all, 

 but is entirely contained within the notch between the postglenoid and post- 

 tympanic processes of the squamosal, and does not extend beneath or in 

 front of the former process. All of the bulla that is visible in the best pre- 

 served specimen is a short, transversely placed, and slightly swollen tube, 

 which projects somewhat below the level of the postglenoid process. Whether 

 this tube really represents the entire bulla, as it appears to do, it is not yet 

 possible definitely to decide. The meatus is relatively large and does not 

 form a complete ring, only the anterior half of the lip being made by the tym- 

 panic, while the posterior half is made by the posttympanic process of the 

 squamosal. So far as I can make out, there is no cancellous tissue within 

 the bulla. 



Undue stress has been laid upon the fact that among existing artiodactyls 

 only the Pecora have the auditory bulla free from cancelli, which occur in 

 the Tylopoda, Tragulina, and Suina. It is altogether probable that this struc- 

 ture has been independently acquired by each of the three last-named groups, 

 for in White River times only Poebrotherium has the cancellous bulla, all 

 the other known artiodactyls of the time, even the peccary-like Perckcerus, 

 having hollow tympanies free from cancelli. The condition of the bulla 

 found in Protylopus seems to indicate that in the main tylopodan series also 

 the cancelli were developed after the series had become well established as 

 such. Concerning the traguline series we have as yet no information, but if 

 the peccaries and camels acquired the structure independently, there can be 

 no reason to doubt that the chevrotains did so likewise. 



The squamosal is large and makes up much of the sidewall of the cranial 

 cavity; inferiorly it forms a shelf which is continuous with the occipital crest, 

 overhangs the auditory meatus, and in front passes into the zygomatic pro- 

 cess. The glenoid cavity is a smooth, slightly convex, and indistinctly marked 

 surface, but the postglenoid process is large, thick, and prominent, forming a 

 high, transverse ridge. The posttympanic is also well developed, extending 

 down nearly as far as the postglenoid and enclosing with it a deep notch, 

 which receives the tympanic. The zygomatic process is slender and rather 

 short, extending outward but moderately from the side of the skull. 



The jugal is quite long, reaching posteriorly almost to the glenoid cavity, 

 and is but slightly notched to receive the zygomatic process of the squamosal. 

 The inferior edge of the orbit is prominent, but the postorbital process is 

 quite low and is widely separated from that of the frontal. The masseteric 



