SOME INTERNAL STRUCTURES 



covering 



skull and not a 

 also, as in other mammals ; 

 this, at any rate, applies to 

 the majority. In the extinct 

 Zeuglodonts, which in many 

 other respects conform to a 

 more generalised mammalian 

 condition, these bones are, 

 so to speak, normal ; but 

 among the toothed whales 

 they do not meet above, 

 and the part of the roof of 

 the skull which should be 

 occupied by the parietals 

 is invaded by the huge 

 supra-occipital. This does 

 not, however, apply to the 

 whalebone whales, though it 



o 



appears to do so. In these 

 whales the foetus has normal 

 parietals meeting above ; in 

 the adult the upper portion 

 of the bones is overlaid by 

 the supra - occipitals. We 

 have here the first stage 

 in the disappearance of the 

 median portion of the parie- 

 tals ; being overlaid by the 

 supra-occipitals their function 

 ceases, and, in accordance 

 with what is always found in 



