142 MICROTIN^ 



In the newborn animal the distance between the squamosals in 

 front is roughly equal to twice the interorbital breadth ; in the 

 adult the space between these bones is diminished, being no 

 greater and often less than the interorbital breadth. In the 



Fig. 69. — Dicrostonyx grcenlandicus Traill. 



Dorsal, ventral, and lateral views (enlarged) of the skull. The small out- 

 line is a natural-sized representation of the skull in dorsal view. 



adult each squamosal develops a strong, prominent, peg-like 

 post-orbital process, which gives origin to a tendinous portion of 

 the temporal muscle. Posterior portions of squamosals very 

 broad, forming practically the whole of the large supratympanic 

 fossse; supratympanic fenestra very small. Inferior portions 

 of lambdoid crest, i.e., all below the supratympanic fenestra 



