226 THE AMERICAN NATURALIST. (VoL. XXXIII. 
there is nothing but membrane bone. Besides, the proper posi- 
tion for the quadrate is at the proximal end of Meckel’s carti- 
lage. But Meckel’s cartilage extends far back of the glenoid 
fossa, and one cannot readily imagine any reason for the trans- 
fer of the quadrate from one position to another. In a word, it 
is as incumbent upon those who claim that the quadrate has 
been lost in the squamosal region as upon those who recognize 
the quadrate in the incus, to explain the formation of a new 
articulation in the mammals. 
An easily accessible figure will illustrate these points: Fig. 
254 on p. 467 of Bell’s translation of Gegenbaur’s Comparative 
Anatomy. If the articulation of the lower jaw of mammals be 
homologous with that of lower vertebrates, then Meckel’s carti- 
lage (#) should run up into the glenoid fossa. If the incus (z) 
be the proximal end of Meckel’s cartilage, then the quadrate 
should be sought between it and the cranial wall immedi- 
ately adjacent. It is difficult to imagine how the quadrate 
could be translated from the point crossed by the “leader” 
from z to a point in the glenoid fossa crossed by the “leader ” 
from /. 
If, on the other hand, we suppose that the proximal end of 
Meckel’s cartilage be represented by the body of the malleus, 
then the incus is in just the proper position for the quadrate ; 
and the proportionally large size of this element in its earlier 
stages shows that it must have been of large size in the ances- 
tral form. Then, again, in the embryo this incus acts as a true 
suspensorium of the lower jaw, while its connection with the 
stapes is of secondary size. In short, it fulfills every condition 
demanded of a quadrate in position and relation to other parts, 
and we doubt if its nature would have been questioned were it 
not for the hypothesis that the mammals had descended from 
the theromorphs in which the squamosal as well as the quadrate 
enters into the formation of the articular surface for the lower 
jaw. 
One objection to the view that the incus is the quadrate is 
based upon the fact that it does not appear from the first as a 
discrete element, but is differentiated from a continuous stroma. 
This objection loses much of its force when we consider that 
