ART. 19 A MIOCENE PORPOISE PROM MARYLAND — KELLOGG 13 



and closes over the area through which the olfactory nerves originally 

 found passage. The mesethmoid is incomplete but probably did not 

 rise to the level of the premaxillae as on the skull of Sotalia tucuxi._ 

 This continuous sheet of bone, consisting of the ectethmoids and the 

 mesethmoid, also sheathes the dorsal and the upper halves of the 

 lateral faces of the presphenoid and on the inner wall of each respirar 

 tory passages meets the corresponding margin of the troughlike 

 vomer in Avhich the presphenoid rests edge to edge. 



A slitlike anterior border for the combined respiratory passages 

 is formed by the close approximation of the internal margins of the 

 premaxillae. As mentioned previously, the premaxillae approxi- 

 mate each other so closely behind the premaxillary foramina that 

 they roof over the mesorostral gutter and conceal the anterior ex- 

 tremity of the presphenoid. The presphenoid appears to be rather 

 porous and forms a plug at the proximal end of the mesorostral gut^ 

 ter, but does not rise to the level of the premaxillae above. Thd^ 

 pluglike bone projects above the premaxillae on the skull of Sotalia 

 tucuxi. 



The maxillae and premaxillae constitute the major portion of the 

 dorsal surface of the skull. The antorbital notches are moderately 

 deep and the rostrum appears to be constricted slightly at the base. 

 For a distance of approximately 50 mm. in front of the antorbital 

 notch the outer margin of the maxilla is rounded off. Farther for- 

 ward this rounded edge disappears with the lateral compression of 

 the rostrum, and the maxilla appears to be deeper from a side view. 

 As a result of the attenuation of the rostrum, the maxilla decreases in 

 breadth anteriorly and the sides slope obliquely downward. The 

 maxilla is barely visible from a dorsal view on the distal one-third 

 of the rostrum. Posterior to the antorbital notch the maxilla ex- 

 pands horizontally and overspreads the frontal bones ; the maximum 

 width is attained opposite to the nasal bones. The posterior margins 

 of the maxillae are in contact with the transverse crest of the supraoc- 

 cipital and the posterointernal angles curve upward, but do not quite 

 reach the level of the dorsal surfaces of the nasals. The thin pl^te- 

 like posterior extremities of the maxillae and the corresponding 

 underlying lateral extensions of the frontals roof over the temporal 

 fossae. On the second skull (pi. 6) the outer margins of both maxil- 

 lae are imperfect above the temporal fossae, but are essentially com: 

 plete on the first skull (pi. 2). As regards curvature each maxilla 

 is somewhat depressed opposite to the nasals and slightly convex 

 above the supraorbital process of the frontal ; the concaveness is mpst 

 evident above the temporal fossa. One large or two small foramina 

 W'hich connect with the infraorbital system are present in each max- 

 illa above the temporal fossa and when tw^o are present the posterior 



