CHAPTER III 



THE POSSIBLE FOREEUNNEKS OF THE MAMMALIA 



The relationship of Mammals to Vertebrates lying below them 

 in the scale, their origin in fact, is a much-debated question, 

 with many attempted solutions. To enter into this large 

 question in detail would involve a great deal of useless state- 

 ment of arguments founded upon misleading or upon quite in- 

 accurate " facts." It will perhaps be sufficient if we reflect here 

 the current view most in vogue at the present, i.e. that which 

 would refer the Mammalia to reptiles belonging to the extinct 

 Permian and Triassic group of the Theromorpha (also called 

 Anomodontia). These have been explored lately to a very large 

 extent, and chiefly by Professor Seeley.^ The very fact that a 

 genus Tritylodon, only known by the forepart of the skull, has 

 been called Mammalian and Anomodont by various authors, 

 shows at least the difiiculty of differentiating the two groups when 

 the material for study is imperfect. As a matter of fact 

 these Theromorpha are without doubt reptiles ; they show, for 

 example, a lower jaw formed out of several distinct pieces, of 

 which the articular articulates with a fixed quadrate on the 

 skull. They possess the characteristic reptilian bones, the 

 " transverse," the pre- and post-frontals, and there are various 

 other points of structure which leave no room for doubt as to 

 their truly reptilian nature. There are, however, numerous 

 indications of an evolution in the mammalian direction in all 

 parts of the skeleton, to the more important of which some 

 reference will be made here. It may be as well to clear the 



^ A series of papers in the Phil. Trans, for 1888-96, of wliicli a useful abstract 

 by Professor Osborn was published in tlie American Naturalist, 1898, p. 309 ; see 

 also Cambr. Nat. Hist. viii. 1901, p. 303. 



