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On the Fate of the Quadrate in Mammals. 
which they had to contend against, we may judge an indi- 
vidual by its external appearance in the last resort only ; we 
determine its systematic position far rather from its internal 
organization, as displayed to us by means of anatomy and 
histology, and above all from its embryology. 
The latter lead us to the conclusion that Nemertines have 
probably been derived from Turbellarian-like forms, but that 
after following a line of development over which the Annelids 
had already passed, they diverged from it again in a direction 
of their own. 
Gottingen, Sept. 1889. 
XLYIII. — On the Fate of the Quadrate in Mammals. 
By R. Bkoom, M.B., C.M., B.Sc. 
One of the most troublesome points in the study of the 
descent of the Mammalia is the explanation of the changes 
which have taken place in the structure of the lower jaw and 
in its mode of articulation with the skull. In Amphibians 
and Reptiles the lower jaw is invariably made up of a number 
of pieces and articulates with the skull by means of the 
quadrate. In Mammals the jaw is apparently a single bone 
articulating with the squamosal. What we have therefore to 
explain is, What has become of the quadrate and how has 
the jaw become simplified ? In the present paper I shall 
only deal with the fate of the quadrate. 
Hitherto the majority of comparative anatomists, chiefly 
from the study of the early condition of the visceral arches, 
have agreed in finding the homologue of the quadrate in one 
or other of the auditory ossicles. Gegenbaur, Kolliker, 
Wiederslieim, and Reichert find its representative in the incus, 
while Huxley looks upon the malleus as its equivalent. 
Parker, who has done more than any one else to elucidate the 
development of the skull, after for many years holding the 
same view as Huxley, ultimately came to regard the incus as 
the Mammalian quadrate. 
That the quadrate of the Amphibian or Reptilian ancestors 
of the Mammals should gradually move back from the arti- 
culation of the jaw and degenerate into one of the auditory 
ossicles is improbable ; and there is little doubt but that the 
view has been founded on a misinterpretation of the morpho- 
