20 PROCEEmNGS OF THE NATIONAL MUSEUM vol.69 



creases in depth posteriorly, attainin^if its maximum near the center 

 of the respiratory passacres. The vomer expands horizontally 

 posterior to the respiratory passages, overspreads the anterior border 

 of the basisphenoid, and externally meets the internal plate of the 

 pterygoid edge to edge. Inferiorly the posterior wall of each 

 respiratory passage is thus lined by the vomer and the internal plate 

 of the pterygoid; the lower external border is formed entirely by 

 the pterygoid and the internal Avail by the vomer; the palatine and 

 pterygoid both contribute to the formation of the anterior wall. The 

 construction and relations of the various bones entering into the 

 upper limits of each respiratory passage are discussed in the descrip- 

 tion of the dorsal surface. 



The median region of the basicranium widens posteriorly and is 

 similar in shape to that of Sotalia tucuxi. It is bounded on each 

 side by a continuous wall formed by the internal plate of the ptery- 

 goid anteriorly and by the falcate process of the basioccipital pos- 

 teriorly. The surface of the median area between these lateral walls 

 is slightly concave. The basioccipital is a much wider bone than 

 the basisphenoid, but the suture between these two bones is very 

 indistinct. The posterior extremities of the falcate processes are 

 slightly thickened and are rounded off. The occipital condyles are 

 large and are separated mesially by a deep groove. Between the 

 internal margin of the exoccipital and the posterior margin of the 

 laterally placed falcate process of the basioccipital there is a deep 

 jugular incisure for the passage of the blood vessels comprising the 

 so-called " jugular leash." The ectal orifice of the small hypoglossal 

 foramen appears on the posterior face of the exoccipital above the 

 apex of the jugular incisure. The lower border of the exoccipital 

 is prolonged downward and is slightly thickened to form the paroc- 

 cipital process. In outline the facet on this process is crescentic and 

 is relatively wider than in Sotalia tucuxi. 



The body of the squamosal overspreads the parietal and appears 

 to be excluded internally from the lateral wall of the brain case, 

 since the lower border of the parietal makes its appearance below and 

 internal to it on the external border of the tympanoperiotic recess. 

 The squamosal, iTowever, is firmly attached to the lateral surface of 

 the parietal and its lateral projection or zygomatic process serves as 

 the articular surface for the condyle of the lower jaw. The glenoid 

 articular surface on the inferior face of the zygomatic process is 

 strongly concave, curving upward and forward. The facet is rela- 

 tively wider than in Delpkinodmi dividum. The external border of 

 the glenoid facet follows the curvature of the zygomatic process, but 

 the internal margin is set off posteriorly by a rather deep excavation 

 on the squamosal which undercuts the facet to a more noticeable ex- 

 tent than in Sotalia tucuxi. This fossil slaiU agrees with that of 



