ILLUSTRATIONS 



FIGURE PAGE 



C. Diagram of the genioglossus muscle in pro- 

 nouncing the sound "oo." (After Robinson.) 



D. Diagram of the genioglossus muscle in pro- 

 nouncing the letter "T." (After Robinson.) 



69. — Human Embryo of the Third Week . . 127 



(From Eidmann, after His.) 



Oblique front view of the head, showing mouth, 

 primary upper and lower jaw buds, gill arches and gill 

 slits. 



(From Entw. d. Zahne. . . , Hermann Meusser, Berlin.) 



70. — Old Chimpanzee, Showing Extraordinary 

 Protrusion of the Lips in Anthropoids 



facing 132 

 (From J. A. Allen, from a photograph by Herbert 



Lang.) 



71. — Three Stages in the Development of Human 



Teeth ....... 135 



A. Future tooth-bearing skin still on the surface 

 of the mouth cavity. From a human embryo eleven 

 millimeters long. 



B. Beginnings of the tooth-pouch. From a human 

 embryo sixteen millimeters long. 



(A, B, from Eidmann, after Ahrens. Entw. d. Zdhne. . ., 

 Hermann Meusser, Berlin.) 



C. Beginnings of the pulp cavity. From a human 

 embryo thirty-two and one-half millimeters long. 

 (After Corning, Lehrb. d. Entw. des Menschen, J. F. 

 Bergmann.) 



72. — Central Incisors of Gorilla and Man. 



Enlarged ...... 137 



A. Upper left incisor of young gorilla, palatal side, 

 showing small mammillae on incisal edge, basal swelling, 

 raised marginal rims and low lingual ridges. 



B. Upper left incisor of fossil Neanderthal (Le 

 Moustier), showing mammillate incisal edge, basal 

 swelling and ridges. (After Weinert.) 



xxix 



