78 ON THE REDUCTION OF THE JUGAL IN MAMMALIA. 



that exhibit different hahits of nutrition should prove of greater 

 service for the ehieidation of phylogenetic problems and taxo- 

 nomical difficulties than has hitherto been recognized. 



A similar shrinking of the postorbital due to genetic factors at 

 present unknown Avould appear to account for the disappearance 

 of that bone in the Tlieromorpha. For clearly the suppression of 

 the postorbital cannot be assigned to any teleological i-eason, since, 

 as has been indicated above, the separation of the orbit from the 

 temporal fossa has been reacquired— presumably to meet an 

 evident pliysiological need — by entirely different devices in several 

 orders of modern Mammalia independently. 



