trie] remains of fossil cetaceans 453 



groove. This groove runs diagonally toward the median line, and 

 thence anteriorly along the inner margin of each premaxilla to a 

 point a little in advance of the line of the posterior end of the tooth- 

 row. The posterior ends of the oremaxillae are lacking. 



The maxillae at the middle 01 the rostum are much narrower than 

 the premaxillae (viewed from above, only about half as broad). 

 They taper gradually anteriorly, as do the premaxillae. Posteriorly 

 they increase in breadth gradually, and opposite the posterior end 

 of the tooth-row appear to have been originally about as broad as 

 the premaxillae at the same point. They increase in breadth rapidly 

 posterior to this point, with nearly straight free margins and the 

 upper surface nearly plane, but inclined inward. 



On the upper surface of the rostrum the suture between the 

 maxillae and premaxillae is in a groove, which is traceable throughout 

 the length of the rostrum and appears to have been especially deep 

 at the base of the latter. 



The inferior or palatal surface of the rostrum is flat, and is bisected 

 by a longitudinal triangular median groove, 3 mm. wide and 2 mm. 

 deep at the middle point. This groove is bounded on each side by 

 the sharp inner edge of the inferior palatal surface of the maxilla, 

 which does not curve upward to meet it, as in S. sulcatus. It in- 

 creases greatly in breadth and decreases in depth anteriorly, and at 

 the end of the rostrum fades away altogether, leaving the whole 

 palatal surface flat. 



At the anterior end of the rostrum the premaxillae occupy more 

 than half the palatal surface and form a triangular area between the 

 maxillae. This triangle is greatly prolonged posteriorly, and the thin 

 strips of the premaxillae probably extend in the median groove nearly 

 as far back as the line of the posterior end of the tooth-row, where 

 the vomer appears between the maxillae, but the sutures are not dis- 

 tinct. 



The vomer is visible as a linear slip for a distance of JJ mm. 

 in front of the anterior insertion of the palatine bones, and probably 

 extended 30 mm. further originally, or 107 mm. in all. 



A triangular rugose area 55 mm. long at the base of the maxillae 

 indicates the position of the palatine bones, but the ridges probably 

 do not represent any portion of the bones themselves. Farther 

 hack there is a shallow depression on the palatal surface of the 

 maxillae, laterally. 



The thin inflated portion of the pterygoids is not developed, or 

 may be represented by small pieces, which cannot be joined to the 

 posterior thicker part. The latter, which borders the nares pos- 

 teriorly, is concave externally and convex internally. 



