ART. 14. MARYLAND FOSSIL PORPOISE KELLOGG. 13 



Hence the vomer sheathes the ventral face of the presphenoid and 

 extends upward on either lateral face to meet the descending proc- 

 esses of the mesethmoid. Thus the mesethmoid and the vomer line 

 the internal walls of the nasal passages. Ventrally, the posterior, 

 the external, and the lower portion of the anterior wall of either 

 nasal passage are formed by the internal pterygoids. Each internal 

 pterygoid is in contact posteriorly with the vomer and anteriorly 

 with the ascending process of the palatine. The anterior wall of 

 either nasal passage superiorly is thus formed by the ascending 

 process of the palatine externally and by the posterior margin of 

 the maxilla internally. The premaxilla contributes the upperniost 

 portion of the anterior wall and limits the dorsal extension of the 

 ascending process of the palatine. As remarked above, the internal 

 pterygoid curves around the nasal passage and establishes the lower 

 boundary of the passage. 



It is difficult to determine whether or not the back of this skull 

 originally resembled Lijmtes although the curvature of the maxillae 

 as far as preserved suggests that the dorsal surface of this skull 

 must have conformed to that type of cranium. If our interpretations 

 are correct the temporal fossae were roofed over to a large extent 

 by the frontal plates of the maxillae. The maxillae increase in 

 width from the tip of the rostrum posteriorly; they attain their 

 greatest width behind the orbit. When the maxillae reach the 

 maxillary notches they push back over the frontals and expand 

 laterally to form the so-called frontal plates. The outer edge of 

 either maxilla is turned abruptly upward and is closely appressed to 

 the internal face of the " up-ended " supraorbital process of the 

 frontal. This maxillary crest makes a right angle with the hori- 

 zontal frontal plate of the maxilla; it terminates abruptly at the 

 posterior end of the supraorbital process for the broken edges of the 

 horizontal frontal plate of the maxilla adhere to the base of that 

 process on the left side of the skull. 



The small fragment comprising the adjoining portions of the 

 frontals and supraoccipital represents all that is known of the back 

 of the skull. This fragment is very important for it shows that the 

 vertex of the skull was not strongly elevated or at least no prominent 

 protuberance, like in Inia or Lipotes, was present. It is also evi- 

 dent that the maxillae were in contact with the supraoccipital and 

 that their internal margins overlapped the frontals on the vertex of 

 the skull. The breadth of the combined frontals^ on the vertex is 

 narrower than the greatest distance between the outer walls of the 

 nasal passages. The posterior end of the right nasal is present; It 

 is closely appressed to the frontal and apparently slopes obliquely 

 forward. From this it appears that the elevation of the vertex of 

 the skull in Inia and Lipotes has been accompanied by the nasals 

 5506— 24— Proc.N.M. vol.03 16 



