AND MESOPLODON SOWEKBYI. 767 



Cetacea. Its convex superficial aspect was comparatively smooth ; from the 

 antero- external thin border a tongue-like curved process projected forward ; 

 whilst the opposite rounded border was crenulated. The bone corresponded 

 closely in form with the tympanic bone of Hyperoodon. 



The parietal bone was small in size, and seemed not to extend beyond the 

 temporal fossa, a portion of the floor of which it formed. The suture along its 

 upper border was, however, too faint to enable the exact extent of the bone to 

 be accurately observed. 



The great lateral crest of the cranium was formed by the narrow free border 

 of the frontal appearing between the superior maxilla and the supra-occipital. 

 Above the orbit, however, the frontal widened out to form an arched roof for 

 that chamber, and terminated both in front and behind in a process — the pre- and 

 post-orbital. A large canal, obviously the optic, opened into the deeper part 

 of the orbit. One inch in front of this canal was an oval opening leading into 

 a deep fossa, into which two canals opened, one leading backwards into the 

 cranial cavity, the other forwards to the great maxillary foramen. These canals 

 doubtless served for the transmission of the ophthalmic and superior maxillary 

 nerves. 



But a small part of the great wing of the sphenoid appeared on the under 

 aspect of the skull, as it was extensively overlapped by a thin plate of the 

 pterygoid. A portion of this wing, however, ascended into the temporal fossa, 

 and articulated with the squamoso-temporal, parietal and frontal. This fossa 

 had no great size, but possessed some depth. It was bounded by the frontal 

 with its post-orbital process, by the zygomatic and by the ex- and supra-occipitals. 



The malar consisted of a rough plate of bone intercalated between the superior 

 maxilla and the lachrymal, and of a flat, smooth, slender process, which passed 

 backwards for a short distance to form the lower boundary of the orbit. This 

 process was broken on both sides of the skull, so that its proper length could 

 not be ascertained. 



The lachrymal was a large plate-like bone, which closely articulated with the 

 orbital surface of the frontal, and entered into the formation of the anterior 

 part of the roof of the orbit. Its anterior border was wedged in between the 

 malar, superior maxillary, and frontal bones. 



With the exception of the meso-rostral bone, the petro-tympanics, the nasal 

 septum, and the pre-maxillse, the bones of the skull were of a loose spongy 

 texture, even on their surfaces — a circumstance which will, doubtless, account 

 for the mutilated condition of almost all the crania of this Ziphioid which have 

 come under the notice of the anatomist. 



The lower jaw consisted of two lateral halves anchylosed at the symphysis. 

 Viewed in profile, the upper and lower borders were concavo-convex. The 

 concavity on the upper border was partly on a line with and partly behind the 



VOL XXVI. PART IV. 9 O 



