Famity LAGOMYID. 
The dentition of the Pikas (Lagomyide) closely resembles that of the 
Hares (Leporide), with which family they were for a long time associated. 
In other. respects, however, the two groups differ widely. In the Pikas, the 
dorsal outline of the skull is gently arched, the occipital portion being but 
slightly below the plane of the interorbital region, instead of being greatly 
depressed, as in the Hares. The orbits are much smaller and open more 
upwardly, and the zygomatic processes arise at a much higher level; the 
axis of the malar bone is rather above the middle of the skull instead of much 
below it. The postorbital processes, so largely developed in the Hares, are 
wanting, and the malar bone is prolonged far beyond the posterior zygomatic 
process, reaching nearly to the auditory opening. In general form, the skull 
is depressed or flattened, greatly expanded posteriorly, and narrowed anteriorly. 
There is a well-developed sagittal crest posteriorly, and the interparietal does 
not form a raised tabular platform as in Lepus. The facial portion of the 
maxillaries is pierced by a single large opening instead of by numerous small 
ones. The auditory bulla are greatly expanded, and open laterally by a 
large orifice, instead of upwardly and posteriorly. The foramen magnum 
is relatively much larger, and the paroccipital processes, so prominent in 
the Hares, are undeveloped. The pterygoid processes are much as in 
Lepus, but’ their wings are more divergent and inclose broader fosse. 
The basi-sphenoid is not perforate, and is not separated by a_ fissure 
from the vomer. The anterior incisive foramina are small, oval, and 
open near the base of the incisor tecth. The palatal portions of the inter- 
maxillaries nearly mect along the mesial line, and have not the deep lateral 
sinuses seen in Lepus. The palate, as in Lepus, forms only a narrow bridge, 
but it is situated more posteriorly, and is wholly devoid of the pointed anterior 
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