314 MR. W. H. FLOWER ON THE OSTEOLOGY OF THE SPERM-WHALE. 
column, and insufficient spaces left between the bones; so that even these measurements 
afford but an approximative comparison. 
Cranium. 
In no known mammal does the cranium depart from the ordinary type to such an 
extent as in the Cachalot. The expansion, elongation, flattening, and distortion of 
many of the cranial and facial bones, met with in a certain degree in all Cetaceans, is 
here carried so far as to render it by no means easy, at least in the adult animal, to 
recognize their homologies. Comparison with the skulls of young individuals and of 
less-modified cetacean forms, however, clear up most of the apparent difficulties. 
The size of the skull in the adult animal is larger in proportion to the remainder of 
the body than in any other known mammal*, As in all animals in which the great 
bulk of the skull is made up of the face and jaws and not of the brain-case, the rela- 
tive size of the entire head increases with age, at all events up to maturity; and it is 
probable that the jaws continue to augment in size and weight after the growth of most 
other osseous structures has ceased. The relative length of the cranium to the vertebral 
column (the vertebre being placed in contact) in the Sydney skeleton (according to 
Wall) is as 46 to 100, in the Tasmanian as 57, in the Caithness as 60, and in the York- 
shire as 67 to 100. ‘The first is scarcely more than half-grown, the second adolescent, 
the last two adult. 
As seen in the section, Pl. LVI. fig. 1, the cerebral cavity is of comparatively limited 
dimensions, being of a somewhat spherical form, with an average diameter of about 10", 
and a capacity of 900 cubic inches. In front of this stretch out horizontally the 
enormously developed bones of the upper jaw, to which the great size of the entire skull 
is mainly due; while rising above it is the high, compressed, vertical, transverse wall 
of bone forming the great occipital crest, the posterior boundary of the enormous 
supracranial basin, so remarkable a feature in this singular skull. 
The general form of the cranium may be compared to that of a huge pointed slipper, 
with a high heel-piece, and the front part trodden down. The lower surface is remark- 
ably straight and flat, though sloping upwards at the sides. The outline, seen from 
above, is long and narrow, rounded behind, maintaining a tolerably uniform breadth for 
the posterior two-thirds of its length, and acutely poited at the anterior extremity, 
The upper surface is, except quite in front, concave, the vast hollow in which the so- 
called ‘ head-matter” of the whalers (composed of nearly pure spermaceti) lies being 
limited behind by the occipital crest, continued laterally into the elevated edges of 
the broadly expanded maxille, which rise from the median line towards the margin of 
the skull, instead of falling away as in most Cetaceans. The great breadth of these 
bones in front of the antorbital notch takes away the appearance of a distinct rostrum 
or beak, generally characteristic of the long-snouted dolphins. 
* The skull of Balena mysticetus is rather longer in proportion to the vertebral column, but it is less massive. 
