6 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. 03. 



In the temporal fossa the external pterj^goid lies below the ali- 

 sphenoid and is in contact with the squamosal. In either temporal 

 fossa the parietal is suturally united with the squamosal posteriorly, 

 with the small alisphenoid inferiorly, and with the frontals ante- 

 riorly. The parietals, which instead of being excluded from the 

 vertex of the skull as in some of the living whalebone whales, meet 

 behind the frontals and form the narrow isthmus connecting the 

 occipital portion of the skull with the pretemporal. As a whole the 

 exposed surface of the parietal widens toward the vertex from the 

 sphenoidal fissure. 



In most cetaceans at least two foramina are visible in each tem- 

 poral fossa. Parietohalaena^ apparently, does not possess all of these 

 foramina and may possibly have retained a more primitive method 

 of affording exit to the cranial nerves. Slightly in advance of the 

 zygomatic process is the foramen ovale whose aperture is seen at 

 the anterior bifurcation of the squamosal. Above and in front of 

 this foramen is the very large sphenoidal fissure, an excavation in 

 the wall of the cranium. Through this fissure the optic and the 

 second division of the fifth nerves probably emerged. The ala 

 temporalis or alisphenoid is preserved on either side, and its extrem- 

 ity appears in the wall of the temporal fossa above the external 

 pterygoid. 



A complete osseous roof for the orbit is afforded by the supra- 

 orbital plate of the frontal. The postorbital projection of this plate 

 is longer than the preorbital and, originally, may possibly have been 

 in contact with the zygomatic process of the squamosal. This, how- 

 ever, is doubtful for the postorbital projection of the frontal bears 

 no articular surface which would suggest such a contact. The supra- 

 orbital plate is convex above and concave below. It is thus evident 

 that the supraorbital plate of the frontal has a more arched form, 

 and in particular is relatively longer transversely than in Patrio- 

 cetus. 



The exoccipitals are flattened up against the squamosals and from 

 a side view are concealed by the squamosals. 



VenPral view. — The basioccipital is a relatively narrow bone with 

 ventral surface concave from side to side. On each side and near the 

 condyles is a prominent subhemispherical protuberance whose poste- 

 rior face slopes obliquely forward and is conspicuously concave. 

 On account of these knoblike lateral processes the basioccipital bears 

 a close resemblance to the same element in the basicranium of 

 CetotheTiurn. 



Anterior to the lateral protuberance on the left side is the posterior 

 end of the imperfectly preserved internal pterygoid. The basi- 

 cranium was broken during removal from the cliff and some of the 

 bones and sutures were thus damaged or destroved. The suture be- 



