OUR ANCIENT RELATIVES 



eral grade of organization described above, it is 

 surprising that in the side view of the skull the 



Fig. 28. Skulls of (A) Advanced Mammal-like Reptile and 

 (B) Modern Opossum. 



For details, see p. xvii. 



higher structural level of the opossum is indicated 



chiefly by the few conspicuous features figured 



below (Figs. 48-52). The jaw muscles of the 



opossum now cover the parietal and part of the 



49 



