MIOCENE PORPOISES — ^KELLOGG 107 



half way in its height is deflected forward horizontally in consequence 

 of the bulging forward of the anterior wall of the braincase, and then 

 drops almost vertically to the interpterygoid space. The shelf that 

 is thus formed in each passage some 25 mm. below the level of the 

 premaxillary on the anterior rim is approximately equivalent in size 

 to the circumference of the corresponding nasal passage; the almost 

 vertical lower portion of each passage is for the most part hidden when 

 viewed from above. 



The maxillaries and premaxillaries constitute the major portion of 

 the dorsal surface of the skull. For a distance of 30 mm. in front of 

 the antorbital notch, the outer border of the maxillary is compressed 

 dorsoventrally and also is concavely depressed dorsally in the region 

 between the antorbital notch and the maxillary foramina. Immedi- 

 ately in front of this basal swelling, the maxillary from a side view 

 abruptly increases in dorsoventral diameter, the convex curvature of 

 the upper surface becomes flattened, and the slope from the pre- 

 maxdlary-maxillary suture gradually becomes steeper. As a result 

 of the attenuation of the rostrum, the maxillary decreases in breadth 

 and depth anteriorly, and is barely visible from a dorsal view near 

 its distal end. Posterior to the antorbital notch, the maxillary 

 expands horizontally and overspreads the frontal bones. This thin 

 ascending maxillary plate, however, does not completely sheath the 

 supraorbital process of the frontal, a strip of the outer border of the 

 latter 10 to 17 mm. in width being exposed above the orbit. In 

 front of the orbit and external to the antorbital notch, the antero- 

 external angle of the ascending plate of each maxillary is produced, 

 forming an apophysis, which overspreads the underlying enlarged 

 lachrymal bone. This flattened lachrymal bone is actually wedged 

 in between the preorbital portion of the supraorbital process and the 

 overlying ascending plate of the maxillary. The maximum width 

 of the ascending plate of the maxillary seems to have been attained 

 at the level of the antorbital notch, but this is uncertain in view of 

 the apparent incompleteness of the outer border of the ascending 

 plate of both maxillaries (fig. 1) above the temporal fossae. The 

 posterior borders of the maxillaries are thrust backward against the 

 curved dorsal crest of the supraoccipital and consequently the postero- 

 internal border of each maxillary is bent upward for a height of 

 approximately 22 mm., the dorsal edge projecting slightly above the 

 level of the posterointernal angles of the frontals, which are exposed 

 on the vertex. The thin and transversely curved ascending plates 

 of the maxillaries and the corresponding underlying lateral exten- 

 sions of the frontals probably did not completely roof over the 

 temporal fossae (fig. 1). As regards curvature, each maxillary is 



