OUR FACE FROM FISH TO MAN 



reptiles of South Africa, This interesting form 

 {Mycterosaurus) was carnivorous, like other pro- 

 gressive reptiles, but had not become too far 

 specialized in this direction. 



The most remarkable feature of its skull is a 

 circular hole on the side of the skull behind the eye. 

 This perforation in the bony mask of the temporal 

 region was the first foreshadowing of the "tem- 

 poral fossa" of the human skull. 



As to the origin of this opening, studies on recent 

 and fossil skulls of many kinds of reptiles indicate 

 that the perforation arose through the progressive 

 thinning of the bone, due to the absorbent action 

 of the membranes surrounding the jaw muscle, 

 which was attached to its inner surface. Mean- 

 while, in resistance to the stresses induced by the 

 same muscle, the borders of the muscle area became 

 strengthened into bony bars or ridges. 



The bony tract below the temporal opening dis- 

 tinctly prophesied the mammalian zygomatic arch, 

 the cheek bone of man. 



Another progressive character of Mycterosaurus 



is the vertical growth of the upper jaw bone 



(maxilla), which up to that time had remained a 



shallow bar in front of the eyes. In the lower 



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