411 
Fate of the Quadrate in Mammals . 
a very short flattened bone with a ball-like articular surface 
on the palatal aspect of the head.” 
In the Reptilian branch of descendants the quadrate gradu- 
ally became more powerfully developed to give a firmer arti- 
culation to a snapping jaw. Still, in the primitive reptiles 
we find the quadrate but feebly developed. In Dicynodon 
we find it as a comparatively small bone so feebly articulated 
with the descending process of the squamosal and the ptery- 
goid that it is lost from many of the British Museum speci- 
mens. Even in Ichthyosaurus , which is well advanced along 
the Reptilian line, w T e still find a small quadrate. 
In the Mammalian line of descent, with the development of 
flexible muscular lips and cheeks a looser articulation of the 
jaw became advantageous. The short flattened quadrate with 
the rounded articular surface was doubtless gradually trans- 
formed into a flattened bony plate, giving great freedom of 
movement to the condyle of the jaw. In process of time 
nature found an equally firm and more elastic medium of 
articulation in an unossified quadrate, which remains in the 
Mammals of to-day as the Inter articular Cartilage . 
The condition of affairs in the skull of a monstrosity I 
recently described* would seem to favour this view as against 
the other theories advanced. In this specimen there is no 
trace of a lower jaw, and the only part of the first visceral 
arch to be detected is an irregular piece of bone about half 
the size of the malleus, representing the fused palatines and 
pterygoids. The zygomatic portion of the squamosal, though 
altered in shape somewhat, is unusually well developed, while 
the tympanies are present as a powerful arch of bone stretching 
from one side of the skull to the other. It is difficult to 
believe that either squamosal or tympanic can represent part 
of an arch whose development is in its other parts so completely 
arrested. 
Should the present theory be confirmed by further research, 
the Interarticular Cartilage might appropriately be called the 
u Quadrate Cartilage.” 
* u On the Condition of the Auditory Ossicles of a Synotic Cyclopian 
Lamb,” Trans. Nat. Hist. Soc. Glasg. 1888-89. 
