V 



26 LOWER JAW CHAP. 



ossification may be added). The angular, splenial, and all the 

 other elements of the reptilian jaw have vanished, though the 

 numerous points from which the mammalian dentary ossifies 

 is a reminiscence of a former state of affairs ; and here again 

 an occasional continuance of the separation is preserved, as the 

 case observed by Professor Albrecht of a separate supra-angular 

 bone in a Eorqual attests. Among other reptilian bones that are 

 not to be found in the mammalian skull are the basipterygoids, 

 quadrato-jugal, and supra temporal. A few of these bones, 

 however, though no longer traceable in the adult skull save in 

 cases of what we term abnormalities, do find their representatives 

 in the foetal skull. Professor Parker, for example, has described 

 a supra-orbital in the embryo Hedgehog ; a supratemporal also 

 appears to be occasionally independent. 



In the mode of the articulation of the lower jaw to the skull 

 the Mammalia apparently, perhaps really, differ from other 

 Vertebrates. In the Amphibia and Eeptilia, with which groups 

 alone any comparisons are profitable, the lower jaw articulates 

 by means of a quadrate bone, which may be movably or firmly 

 attached to the skull. In the mammals the articulation of the 

 lower jaw is with the squamosal. The nature of this articulation 

 is one of the most debated points in comparative anatomy. 

 Seeing that Professor Kingsley l in the most recent contribution 

 to the subject quotes no less than fifty-two different views, many 

 of which are more or less convergent, it will be obvious that in a 

 work like the present the matter cannot be treated exhaustively. 

 As, however, Professor Kingsley justly says that " no single bone 

 occupies a more important position in the discussion of the 

 origin of the Mammalia than does the quadrate," and with equal 

 justice adds that " upon the answer given as to its fate in this 

 group depends, in large measure, the broader problem of the 

 phylogeny of the Mammalia," it becomes, or indeed has long been, 

 a matter which cannot be ignored in any work dealing with the 

 mammals. A simple view, due to the late Dr. Baur and to 

 Professor Dollo, commends itself at first sight as meeting the 

 case. The last-named author holds, or held, that in all the 

 higher Vertebrates it is at least on a priori grounds likely 

 that two such characteristically vertebrate features as the 

 lower jaw and the chain of bones bringing the outer world 

 1 Tufts College Studies, No. 6, 1900. 



