MIGRATION OF TERRESTRIAL VERTEBRATES 305 



and that the centre of the Multituberculata was 

 the European Continent, which was also joined to 

 the first by intermittent connections across the 

 North Atlantic or the Arctic lands. But this 

 rational hypothesis has had to contend up till now 

 with the complete absence of any possible ancestor 

 of the Mammals in the ante-Triassic strata of the 

 Great Boreal Continent. 



The speculations of modern palaeontologists are 

 to-day rather directed to South Africa, where, at 

 the end of the Permian and during the Trias, a 

 whole group of terrestrial Reptiles, the Theromorphs, 

 developed, some of which present curious affinities 

 in certain details of their organism, with the lower 

 Mammals. Thus the Tritylodon, with its upper 

 molars furnished with three rows of rounded tuber- 

 cules, so much recalls the dental characteristics of 

 the Multituberculata that for a long time it was 

 considered a true Mammal, notwithstanding the 

 decidedly reptilian features of its skull. Similarly, 

 the bones of the limbs of the Theriodesmus, which 

 are perhaps those of the Tritylodon, recall, according 

 to Seely, the structure of those of the Lemurians 

 and Carnivora. Other Theromorphs from the 

 Karroo likewise present rather curious mammalian 

 affinities : the Dicynodon in the structure of the 

 pelvis, and the Cynodmco in the form of the humerus, 

 furnished with an inner arterial bridge like that of 

 the Felidse. But, notwithstanding these interesting 

 affinities, which are, perhaps, only adaptations to 

 identical functions, we cannot say that any one of 

 the known Theromorphs can have directly given 

 birth to the first Mammals, and we are forced to 



