FKOM THE rOEEST BED OF EAST EUJS'TON. 167 



prominent median crest along the latter bone. The position of these parietal ridger., 

 depending as they do upon the development of the temporal muscles, would no doubt 

 vary in form in older skulls. The sagittal suture is even shorter than it is in the 

 Beaver, the parietals only joining for about half an inch. The squamosal bone has 

 much the same form that it has in the Beaver; but its parietal margin is more deeply 

 sinuous, and the suture forms a strongly impressed groove along the side of the 

 brain-case. 



On the side of the skull (fig. 3) the squamosal sends down a process from its hinder 

 part between the auditory meatus and mastoid, and it has a large foramen a little 

 behind the jugal buttress ; while anteriorly it ends at the postorbital process. 



The jugal buttress of the maxilla descends from the upper surface of the skull about 

 halfway towards the alveolar margin ; while in the Beaver this buttress extends as a 

 distinct ridge quite to the lower edge of the maxilla. 



The suborbital foramen is situated as it is in the Beaver, but the plate of bone by 

 which it was covered is partly broken away on both sides. This plate of bone in the 

 Beaver is developed anteriorly into a strong ridge for the attachment of muscles ; and 

 judging^ from the still larger process remaining in the fossil below the foramen, the 

 muscles attached in this region were more strongly developed than they are in the 

 Beaver. 



The premaxilla in the fossil commences directly in front of the suborbital foramen, 

 and is relatively larger than in the Beaver, being altogether more strongly developed, 

 evidently in relation to the powerful incisor, indicated by the large size of the alveolus. 

 The two premaxillse form in front of the snout a vertical, roughened, triangular area, 

 the upper part of which is separated by a deep transverse groove, and forms a pair of 

 tubercles which encroach upon the lower part of the external nasal opening, and 

 o-ive it a nearly horizontal lower margin: the Beaver's nasal aperture is pointed 

 inferiorly. Seen from below (fig. 2) the premaxillse are broader than in the Beaver, and 

 especially so at their front part : where the two bones meet on the palate they form 

 a median crest, which, dividing, is continued around the palatal foramina, and again 

 uniting extends along the entire length of the palate to the posterior nares. The 

 palatal foramina are elongated slits as in the Beaver, but are differently situated, being 

 about twice as far from the incisors as they are from the anterior grinders, while in the 

 Beaver they are placed about midway between these two points ; and further, in the 

 fossil the maxillo-premaxillary sutures divide these foramina at about their middle into 

 anterior and posterior moieties, the maxillae and premaxillse taking about equal shares 

 in the formation of the apertures; in the Beaver, on the other hand, these sutures are 

 quite at the hinder part of the foramina, which are thus almost wholly formed by the 

 premaxillse. 



The palatal aspect of the maxillse shows very clearly the large size of the processes 

 below the suborbital foramina (so/.), as well as two deep depressions at their bases, 



2b 2 



