ILLUSTRATIONS 



23. — Origin of the Facial Muscles of Man . 42 



A. Primitive reptile (Labidosaurus) with continu- 

 ous bony mask covering skull. (After Williston.) 

 The mask was covered with thick skin without muscles, 

 as in the alligator. 



B. Modern reptile (Sphenodon) with an open or fen- 

 estrated skull covered with thick, non-muscular skin. 

 The seventh nerve (heavy black line) is seen beneath 

 the sphincter colli muscle, a broad band around the 

 throat. (From Fiirbringer, modified from Ruge.) 



C. Primitive mammal (Echidna) in which the 

 sphincter colli system has grown forward over the 

 face. (After Ruge.) 



D. Gorilla. E. Man. (Both after Ruge.) 



24. — Diagram Showing the Chief Branches of 



THE Facial Nerve ..... 44 



A. Gorilla. (After Ruge.) 



B. Man. (After Weisse.) 



25. — Successive Dominance of the Amphibians, 



Reptiles, Mammals and Birds, Man . 46 



26. — The Common Opossum, a "Living Fossil" 



FROM THE Age of Dinosaurs . . facing 46 



27. — Skull Parts of Extinct Opossum (Eodelphis) 



from the Upper Cretaceous of Montana 48 



Superposed on outlines of skull of recent opossum. 



28. — Skulls of (A) Advanced Mammal-like Rep- 

 tile (Ictidopsis) FROM THE Triassic of 

 South America and of (B) a Modern 

 Opossum ....... 49 



29. — Long-snouted Relatives of Ours from the 



Cretaceous of Mongolia ... 50 



A. Skull of Deltatheridium pretrituberculare. Nat- 

 ural size. 



xvii 



