INTRODUCTION 



17 



profoundly affected and diversified, and numbers of types are evolved, as, 

 for example: 



Ambulatory, slow-moving, mostly primitive. 

 Cursorial, swift-moving, secondary. 

 Saltatorial, swift-moving, leaping, secondary. 

 FossoRiAL, slow-moving, digging, and burrowing. 

 Natatorial, amphibious, aquatic, swimming. 

 Arboreal, slow-moving, tree-climbing. 

 Glissant, gliding, as in the 'flying' squirrel. 

 Volant, flying, as in the bat. 



Primitive and progressive skull structure. — Changes in tooth proportion 

 and foot proportion may or may not be accompanied by changes of propor- 



c&i) 



Fig. 7. — Skull proportions among Titanotheres. A. Brachycephaly, short-headed, 

 Palasosi/opfi major. B. Mesaticephaly, medium-headed, Manteoceras manteoceras. C. Doli- 

 chocephaly, long-headed, Dolichorhinus cornutus. 



tion in the skull. Here again we find that there are three general stages 

 in the anatomy of the skull of mammals,^ and that the descriptive terms are 

 the same as those which were introduced long ago (1842) in the anatomy 

 of the human skull by the great Swedish anthropologist, Anders Adolf 

 Retzius (1796-1860), namely: 



Mesaticephaly, an intermediate or partly elongated condition, charac- 

 teristic of many intermediate and primitive forms, such as the tapir. 



' See Osborn, H. F., Dolichocephaly and Rrachycephaly in the Lower Mammals. Bull. 

 Amer. Mus. Nat. Hist., Vol. XVI, Art. Vll, Feb. 3, 1902, pp. 77-89. 

 C 



