6 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 72 



but the maxillary as well. The cartilaginous nasal partition, the 

 mesethmoid, has a tendency to ossify. The incisive foramen is 

 narrowed and closed. In the palate the maxillary pushes itself far 

 backward, forcing the palatine behind it ; the palatal surface of the 

 palatine is thus shortened. But at the same time the maxillary acts on 

 the palatine in such a way that it also increases in thickness. The 

 braincase is acted on from the front by the pressure of the water 

 against the forehead ; from behind it is pressed by the cervical 

 vertebrae and the neck muscles. In this manner it becomes so 

 squeezed that it acquires a short, broad form. Pressure is exercised 

 especially on the frontal and on the supraoccipital and interparietal. 

 These bones widen out at the expense of the parietal, whose inner- 

 most part is squeezed quite narrow and eventually obliterated. The 

 exoccipital also grows, especially noticeably downward, where it 

 broadens out shield-like behind the mastoid and the tympanic. The 

 mastoid is compressed inward between the exoccipital and the 

 squamosal, by both of which it is so overgrown that at last it is no 

 longer visible on the outer surface of the braincase. 



The water pressure on the head from in front has also a great 

 influence on the soft parts of the face and through them on the skull. 

 It assists in shifting the nasal apertures. The cetacean has tried, with 

 the help of the nose muscles, to draw the apertures as high as possible 

 up on the head's upper side, in order to be able easily to get them 

 raised above the water. The result has been that the nasal cartilage 

 has caused resorption of the anterior border of the nasal bones and 

 has forced them further and further back. The cartilage has also 

 worked itself back between the anterior median part of the frontals, 

 pushing the plates of the ethmoid behind it. Thus at last the nares 

 have acquired a position which appears to be on the forehead but 

 which in reality is close in front of the anterior wall of the braincase. 

 The moving of the nasal cartilage has been accelerated in those cases 

 where the facial adipose cushion which originally lay in front of the 

 nares and which in the first place was merely a little filling out of 

 fatty connective tissue has been stimulated to growth by the pressure 

 of the water, becoming very large, pushing the nasal cartilage back- 

 ward, pressing it against the front wall of the braincase and disinte- 

 grating the nasal bones and the plates of the ethmoid. The nasals then 

 become tuberformed and are pressed into the frontals. The adipose 

 cushion together with the nasal muscles and other neighboring 

 structures may exercise an enormous influence on the skull, the 

 anterior and upper sides of which it modifies to form its bed, the 

 " facial depression." 



