38 THE MAMMALIAN ORDER PRIMATES [SECT. A 



mammal-like Reptiles Cotylosauria and Therocephalia. The defi- 

 niteness of this part of the history (also the absence of any 

 suggestion of Amphibian relations), must be specially remarked. 

 For in spite of their "mammalian" characters the omission of these 

 particular Reptiles has been proposed. Of these characters the 

 most important (on account of the preservation of the parts in 

 fossil examples) relate to the joint between the lower jaw and the 

 skull. Reference has been made already (p. 19) to this joint, 

 and to the reduction of the quadrate bone in Mammals. The 

 arrangement shewn in the diagram, placing the Permian Reptiles 

 in the line of descent, commands a large balance of expert opinion. 

 Hubrecht (1897) and Kingsley (1900) seem to be the most promi- 

 nent of those who prefer to exclude these and more modern 

 reptilian forms from a place in the line of Mammalian ancestry. 



The Prototheria (Monotremata) are made to diverge even in 

 the Triassic period, but this is a matter of speculation only, since 

 the only extinct Prototherians known so far are derived from very 

 late (Post-Tertiary) cave-deposits in Australia. 



The point of divergence of the existing Orders of Marsupials. 

 (Diprotodontia and Polyprotodontia) is placed with confidence in 

 the Jurassic period. After this comes an area in which the 

 evidence is scanty and equivocal, marked by the indication " Un- 

 discovered Placentals." But when this region of " Cretaceous 

 uncertainty " has been passed, the early phases of the Tertiary 

 period are marked by a perfect explosion of Eutherian forms. 

 Here we are interested chiefly in a group to the right side of the 

 diagram and the lines may now be traced from the periphery 

 inwards. The Lemuroidea and Anthropoidea are there shewn 

 to be joined as the Primates (not marked) ; the latter stem springs- 

 from a branch common to it and the Dermoptera (with the Cheiro- 

 ptera) on the one side, and the insectivorous Tupaioidea on the 

 other. This common branch represents the Super-order Archonta 

 (v. supra, p. 26), and its own origin is found almost at the root of 

 all the Eutherian stocks. 



Of the various Eutherian Orders, it thus appears that the 

 Primates, Cheiroptera, Dermoptera, and Tupaioidea (formerly a sub- 

 division of the Insectivora, and now separated as the Order Meno- 

 typhla) are associated with the Insectivora (Soricoidea, etc.) and 



