REPORT ON THE CETACEA. 7 



Eacli superior maxilla in the young skull extended to 2| inches from the tip of the 

 beak where it terminated as a slender bar of bone. In both crania it expanded 

 posteriorly, and, overlapping the frontal bone, ascended to the vertex behind the prse- 

 maxiUa. The anterior surface of its cranial exj)ansion was concave, and the hollow was 

 somewhat deeper in the adult than in the young specimen. In the young a large single 

 foramen was in the right bone almost on a line with the preemaxillary foramina, but in the 

 left bone were two foramina. In the adult four foramina, one of which was partially 

 subdivided, were in the right bone, but only two in the left. In both skulls a large 

 foramen, directed outwards, opened in the expanded cranial portion, on a line with the 

 middle of the anterior nares. An ectomaxillary ridge was present in both crania, but 

 in neither so prominent as in Mesoplodon sowerhyi. In the adult the ectomaxillary 

 groove, and the buttress-like projection of the pterygoid and superior maxilla, closely 

 resembled Owen's description of the original skull in the British Museum. In the younger 

 skull, whilst this groove was marked at the base of the rostrum, it disappeared in the 

 anterior two-thirds, whilst neither the pterygoid nor superior maxilla swelled out to form 

 a " buttress," so that instead of the massive piece of bone seen in the adult swelling out 

 laterally beyond the margin of the ectomaxillary ridge, in the young, but a faint eleva- 

 tion occurred, and the ectomaxillary ridge formed the most prominent feature in the 

 outline of this part of the beak. In both crania, as well as in Meso-ploclon soiverbyi, 

 the antorbital notch was separated from the base of the ectomaxillary ridge by an inter- 

 mediate maxUlary tubercle. 



The palatal surface of the beak flattened anteriorly in the adult, but slightly concave 

 in the younger skull was formed by the preemaxillse, which passed backwards between 

 the anterior ends of the superior maxilla, to articulate with the mesial palatal 

 part of the vomer. In the adult, the middle and posterior parts of this surface were 

 much more convex than in the young skull, and the sutures were almost entirely 

 obliterated. In the younger skull, the palatine plates of the two palate bones appeared 

 as narrow triangles between the diverging anterior ends of the two pterygoids, and 

 separated them from the superior maxillas ; but these plates did not articulate with each 

 other mesiaUy as in Mesoj^lodon soicerhyi ; for the superior maxdlse were prolonged 

 backwards between them in order to articulate with the interpterygoid part of the vomer 

 which appeared on the surface in this locality. In the adult, the palate plate of the 

 palate bone was absent, so that the pterygoid articulated directly with the superior 

 maxilla. Both in the adult and j^ounger crania the palate bone passed backwards and 

 outwards on the side of the beak, between the pterygoid and superior maxilla, so as to 

 come into proximity with the malar bone. 



Each pterygoid was a triangular plate of bone, concave externally, and ^dth its lower 

 border everted so as to constitute the lower boundary of a pterygoid fossa ; a deep notch 

 directed upwards and forwards was situated in the base of each plate. The two ptery- 



