PSEUDORCA CRASSIDENS. 
197 
poral fossa which is formed by the frontal bones does not even make one half of the whole 
fossae, and that part of its wall that is formed by the parietal and temporal bones is not con- 
Fig. i. 
cave but convex. Thus, the temporal fossa is, no doubt, less spacious than in the killers, but 
this diminution in depth is partly compensated for by its being extended farther backwards, 
than in the latter Cetaceans, as the continuation of the occipital ridge by which it is limited 
behind, describes a parabolic curve, and not a simple arc of a circle, as in the Orcas (at any 
rate in the Northern species of this genus). In the grampuses and the ca’ing-whales, the tem¬ 
poral fossae are much smaller, and the share which the frontal bone has in forming them is of 
very slight importance, especially in the latter. It is further peculiar to our dolphin, that it is not 
the nasal bones, but, on the contrary, a projecting knob on the interparietal bone, ankylosed with 
the occipital bone, behind the occipital ridge, which forms the uppermost point of the skull; for 
just the contrary is the case in all the three kindred forms. It must further be added that the 
nasal bones do not approach the occipital ridge so nearly as in the latter forms, but are placed 
some distance (about three inches) before it; the reason of this is, of course, that that extremity of 
the interparietal bone jutting out before this ridge, and that strip of the frontal bones which is 
not covered with the superior maxillaries is broader here than in the other three species. It may, 
perhaps, seem unsafe to derive a character from such a peculiarity, as in the Cetaceans, the bones 
of the cranium are frequently modified even considerably in their relative position during 
the growth of the animal; and, in truth, w r e cannot do so even in the allied species of the 
ca’ing-whales, for, when these are young, their nasal bones are almost as far removed from 
the occipital ridge, as in the form here described, whereas, we know that they come very near 
to it when the animal has increased in age. But in our crassidens we need scarcely fear that age 
might produce a similar alteration. For the individuals in question, are not only old animals, 
one of them even unquestionably very old; but a comparison between the latter and the some¬ 
what younger specimen from Middelfart, shows that the distance between the occipital ridge and 
the nasal bones become even rather greater than smaller, as the animal grows older. 
