REPORT ON THE CETACEA. 



The length of the entire cranium of the younger specimen was 2| inches less than 

 that of the beak of the adult. The crest at the vertex in both was formed of the nasals, 

 frontal, supra-occipital, and the upper ends of the prsemaxill^ and superior maxillae, but 

 in the younger specimen a thin lamina of each parietal could be traced upwards to the 

 vertex, where the laminae from opposite sides became fused together (PI. I. figs. 1, 2). 



The beak was about twice as long in the adult as in the young. Its apex in the 

 latter was formed entirely of the two praemaxillse, but in the adult the anterior end of 

 the mesorostral bone seemed to be fused with the tips of the praemaxillaries, though the 

 absence of sutures prevented the exact determination of their place of union. In the 

 adult, the interval between the praemaxillaries was filled up as far as the base of the 

 beak by the solid mesorostral boife, which, as in Professor Owen's description, " rises as a 

 smooth, dense convex ridge, l\ inches across at its broadest part, gradually contracting 

 to a breadth of half an inch, when it has traversed one-thiixl of the length of the 

 rostrum." In the younger skull this bone was absent, and an elongated mesorostral 

 furrow, empty in the macerated skull, was seen. This furrow was occupied in the un- 

 macerated state by a bar of cartilage, and the conversion of this cartilage into the 

 dense mesorostral bone is accompanied by the remarkable elongation of the beak, which 

 constitutes one of the most noticable features of difference in the dimensions of the 

 younger and adult crania. As the beak of specimen B had been sawn through 20^ 

 inches from the tip, the extremely dense porcellaneous character of the mesorostral bone, 

 and its intimate fusion with the vomer, the superior and praemaxillary bones were seen 

 on the surface of section. Whilst the vomer and praemaxiHae partook of the same 

 porcellaneous character as the mesorostral bone, the superior maxiUas again possessed a 



