Fate of the Quadrate in Mammals. 411 



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- 

 gold that it is lost from many of the British Museum speci- 

 mens. Even in Ichthyosaurus^ which is well advanced along 

 the Reptilian line, we 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 

 ** Quadrate Cartilage." 



* " On the Condition of the Auditory Ossicles of a Synotic Cyclopian 

 Lamb," Trans. Nat. Hist. Soc. Glasg. 1888-89. 



