AKT. 14. 



THE SKULL OF MEGAPTERA MIOCAENA KELLOGG. 



11 



rather deep groove, into which the inner edge of the wedge-shaped 

 ridge, formed by the fused processes of the basisphenoid and squa- 

 mosal, is received, and which in turn serves to lodge the periotic 

 more firmly. The dorsal surface of thf prootic is closely applied to 

 the petrous portion of the squamosal, while the anterior margin is 

 in contact with the external pterygoid process of the alisphenoid. 



The prootic is not clearly differentiated from the opisthotic, for 

 these elements are so fused as to be unrecognizable as separate ele- 

 ments. 



FlO. 2. rOSTEIUOR VIEW OF LEFT PEr.IOTIC OF MeGAPTEUA NODOSA X 1, CaT. NO. 21492, 



U.S.N.M. ; Caps Cod, Massachusetts. 



The posterior process or opisthotic, as previously mentioned, was 

 broken off when the periotic was removed from the skull for study. 

 The apophysis of the opisthotic fits snugly into the groove that lies 

 just posterior to the open channel for the external auditory meatus. 

 It was impossible to remove the apophysis without doing serious 

 damage to the skull and hence it was not figured with the remainder 

 of the periotic bone. The entire external prolongation of the 

 opisthotic of Megaptera nodosa is not shown in figures 2 or 4. 



On the ventral face of the prootic (fig. 3), near the posterior 

 end, there is a rounded depression to which the pedicle of the anterior 

 extremity of the tympanic bone is ankylosed. According to previous 

 investigators, it would appear that the processus gracilis of the mal- 

 leus is fused with a rounded projection on the tympanic near the 

 posterior end. As most of the posterior pedicle is wanting on both 



