ART. 28 SKULL OF ZARHACHIS FLAGELLATOR KELLOGG 9 



least half of the upper border of the anterior wall of each nasa' 

 passage is contributed by the vomer whose upper margin rolls over 

 or is folded outward so that it meets the maxilla slightly external to 

 the mid line of the nasal passage. The peculiar curvature of the 

 lateral walls of the trough of the vomer around the upper borders of 

 the nasal passages does not appear to be duplicated in an}^ of the 

 living toothed whales. The maxilla contributes the outer v»^all and 

 about one-half of the dorsal border of the anterior wall. Inferiorly, 

 the palatine extends upward in each nasal passage for a distance 

 ec|uivalent to about three-fourths of the depth of the anterior wall 

 and is inserted between the maxilla and vomer in the shape of a 

 subtriangular wedge. The dorsal margin of the surface of the 

 palatine which takes part in the formation of the nasal passage is 

 emarginate. 



In front of the nasal passages, the trough of the vomer assumes the 

 shape characteristic of most dolphins. At the level of the anterior 

 margin of the nasal passages, the greatest depth of the trough of the 

 vomer is 98 mm., but at a point 180 mm. in front of these passages, 

 it does not measure more than 25 mm. in depth. For a distance of 

 75 mm . in front of the nasal passages, the dorsal margins of the lateral 

 walls of the vomer slope forward and downward at a very steep angle. 

 This may be associated with the mesial depression of the internal 

 borders of the premaxillae behind and in front of the premaxillary 

 foramina. Anterior to this depression, the reduction of the lateral 

 walls of the vomer is rather gradual. From a ventral view, the vomer 

 is seen to be split along the mid line of the axial ridge, but this may be 

 abnormal. The axial ridge is wedged in between the opposing faces 

 of the maxillae and in correlation with this compression and with the 

 slope of the internal surface of the maxilla, the floor of the mesorostral 

 gutter is rather narrow posteriorly and it becomes so narrow about 140 

 mm. in front of the nasal passages that it would appear V-shaped in 

 cross section. The lateral border of the trough of the vomer rolls 

 over and is overspread by the thin margin of the horizontal plate of 

 the premaxilla, which overhangs the mesorostral gutter. 



Posterior view. — The back of the brain case (pi. 3) has been crushed 

 in a dorso-ventral direction and the extent of this crushing is best 

 illustrated on the posterior face of the skull. The lower half of the 

 supraoccipital was too thin to support the great weight of the sedi- 

 ments which overlay the skull, and the bone fractured in many direc- 

 tions. A portion of the supraoccipital was thrust downward into 

 the foramen magnum and it also buckled inward above the condyles. 

 The displacement or amount of crushing at the center of the foramen 

 magnum may equal 20 or 25 mm. Another consequence of this 

 crushing is shown by the buckling of the parietals andjfrontals in the 

 temporal fossae. 



54286— 26t 2 



