12 



MICROTIN^ 



Fig. 5. — Arvicola amphibius Linnaeus, 



Lateral views of skulls in different stages of growth. Stages I and II 

 (same sjiecimens as shown in Fig. 1). 



In Figs. 5-7 the progressive flattening of the dorsal surface, the 

 changing direction of the occiput (inclined backwards in Stage J, forwards 

 in Stage VI), the forward migration of the orbit (most marked in Stages V 



