AKT. 10 A MIOCENE PORPOISE FROM MARYLAND KELLOGG 21 



Sotalia tucuxi in the manner in which the ventral surface of the 

 squamosal is excavated and probably also in the shape and direction 

 of the thin projecting falciform process which has been destroyed. 

 This falciform process probably projected inward and forward as in 

 Sotalia; between the base of this process and the temporal angle of 

 the alisphenoid is the semiinclosed foramen ovale. The postgienoid 

 process is small and slightly thickened. A narrow deep groove for 

 the external auditor}^ meatus traverses the squamosal behind the post- 

 gienoid process. A posteriorly directed process of the squamosal is 

 suturally united with the exoccipital along its posterior border. The 

 periotic was attached by ligaments to the squamosal at the origin of 

 the groove for the external auditory meatus. The tympanoperiotic 

 recess is bounded by the squamosal externally, the exoccipital poster- 

 iorly, the falcate process of the basioccipital internally, and by the 

 falciform process of the squamosal anteriorly; the projecting lower 

 border of the parietal, the backwardly projected alisphenoid, and the 

 underlying process of the basioccipital contribute a complete roof for 

 this recess. Unfortunately a portion of the roof of the tympano- 

 periotic recess has been destroyed on the right side, so it is not possi- 

 ble to check conditions observed in the opposite recess. Nevertheless, 

 the roof of the recess on the right side appears to be normal, without 

 any irregularities produced by crushing, and agrees, furthermore, in 

 all essential details with conditions observable on the skull associated 

 with the skeleton. Probably the most noticeable peculiarity is the 

 large posterior lacerated foramen which measures 9 mm. in diameter ; 

 there are no separate compartments for the nerves and blood vessels. 

 The ectal orifice of this foramen is situated fully 28 mm. above the 

 lower margin of the falcate process of the basioccipital. At the base 

 of the falcate process and near the posterior margin of the pterygoid 

 is the small ectal orifice of the canal for the carotid artery. The 

 mandibular branch of the trigeminal nerve issues through a cleft on 

 the posterior border of the alisphenoid and crosses the ventral sur- 

 face of the latter on its outAvard course, although the usual groove is 

 poorly defined. 



The alisphenoid is a narrow bone Avhich curves outward and up- 

 ward, and is suturally united with the parietal above, the frontal in 

 front, and on the rear with the squamosal externally and the parietal 

 internally. Farther forward the orbitosphenoid projects obliquely 

 forw^ard and its extremity is applied to the ventral surface of the 

 supraorbital process. As in Sotalia tucuxi^ the orbitosphenoid forms 

 the lower portion of the anterior wall of the brain case. The sphe- 

 noidal fissure appears to have been closed by the overlapping of the 

 orbitosphenoid by the alisphenoid. Comparison with Sotalia shows 

 that the optic nerve passed outward through a notch on the posterior 

 border of the orbitosphenoid in both. The outward course of the 



