TRUE : THE FOSSIL CETACEAN, DORUDON SERHATUS. 69 



of the latter depends, of course, on the length of the anterior extension 

 of the maxilla which articulates with the premaxilla. As this is lacking 

 in part, the length of the nasal branch of the premaxilla is uncertain, 

 as are also the exact proportions of this region of the skull. 



The left nasal bone is nearly complete, and of the right about one-half 

 remains. It is possible, therefore, to show quite exactly the shape and 

 relative position of these bones. The outer margin is divided unsym- 

 metrically into two parts, of which the posterior is the shorter. This 

 shorter margin appears to articulate with the maxilla, and the longer mar- 

 gin with the premaxilla. The two nasals fit together accurately in the 

 middle, the right one having a superior ledge which lies on an inferior 

 ledge of the left nasal. The median line of junction is somewhat sinuous. 

 The nasals in transverse section are strongly curved, and when joined to- 

 gether in the natural position, form a vaulted roof over the nasal cavity. 

 At the posterior end the inferior surface is marked with coarse, longi- 

 tudinal sutural ridges. 



The detached fragment containing a single tooth, which Gibbes fig- 

 ured in 1847 in his Plate 4, figure 4 (see Plate 1, figure 4, accompany- 

 ing this article), is very important and at the same time rather difficult 

 to interpret. Accompanying the fragment is another of similar size 

 which fits against the root of the tooth and contains the alveolus of a 

 second tooth. After closely studying the tooth which is present, I am 

 of the opinion that the other alveolus belongs in front of it and is that 

 of the first premolar. Anterior to this alveolus is a small, conical piece 

 of bone, which represents the anterior end of the maxilla, so far as it is 

 preserved, but how much is lacking is uncertain, as is also the position 

 of the canine, of which no trace remains. That there was another 

 premolar tooth anterior to the alveolus above mentioned is improbable. 

 That the fragment containing the tooth is from the anterior part of the 

 maxilla, and that the tooth is, therefore, a premolar, is evident from the 

 fact that its external surface is nearly flat, while in the fragment with 

 three teeth, presently to be mentioned (which bears the articulation for 

 the malar at the posterior end and is therefore the posterior part of 

 the maxilla), the external surface is quite convex. The anterior and 

 posterior margins of the crown of the premolar tooth are, I believe, dis- 

 tinguishable, owing to the fact that in all the teeth of Zeuglodon and its 

 allies, as shown by specimens in the N'ational Museum and by the fig- 

 ures of Mtiller, Andrews, and other authors, the accessory cusps are 

 smaller and further from the apex of the tooth on the anterior margin 

 than on the posterior. 



