26 LOWER JAW ; CHAP. 
ossification may be added). The angular, splenial, and all the 
other elements of the reptilian jaw have vanished, though the 
humerous 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 Rorqual attests. Among other reptilian bones that are 
not to be found in the mammalian skull are the basipterygoids, 
quadrato-jugal, and supratemporal. 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 Reptilia, 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 + 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 ina 
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 im 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. 
