Family LAGOMYID^l. 



The dentition, of the Pikas (Lagomyidce) closely resembles that of the 

 Hares (Leporidaf), 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 arc 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, arc 

 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 bullae 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, arc undeveloped. The pterygoid processes are much as in 

 Lepus, but their wings are more divergent and inclose broader fossse. 

 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 teeth. The palatal portions of the inter- 

 maxillaries nearly meet 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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