MR. W. H. FLOWER ON THE OSTEOLOGY OF THE SPERM-WHALE. 315 
- The absence of bilateral symmetry so generally met with in the skulls of toothed 
whales, is carried to its extreme in the Cachalot. It is chiefly manifested in the parts 
around the nasal passages. One of these orifices, the left, is immensely developed, the 
other reduced in a corresponding degree. But the distortion thus occasioned is not 
confined to the bones immediately concerned in the formation of these apertures, it 
affects the entire wall of the great supracranial basin, as seen in the upper view of the 
young skull (Pl. LVII. fig. 1). 
As the individual bones of the foetal Cachalot’s skull have been described by Professor 
Owen *, I will confine my present account chiefly to the structure of the different 
regions of the cranium of the adult Tasmanian specimen, using the young skull from 
the same locality for illustration in cases where the ankylosed state of the former renders 
it impossible to make out the nature of the parts. I will also add some comparisons 
with the Hyperoodon, as one of the most nearly related of the ordinary toothed whales, 
and finally point out such differences as I have observed in the other specimens of 
Cachalot exainined. 
Commencing with the cranial cavity, as the central point around which the whole 
head is developed, and of which a view was afforded by a median section of the skull 
(see Pl. LVI. fig. 1, and woodcuts, figs. 12 and 13, p. 372), its general form is, as said 
before, roughly speaking, spherical, although slightly flattened on its upper anterior, 
and also on its lower posterior aspect. Its greatest diameter is diagonally from below 
upwards and backwards. The extent in this direction is best seen in the woodcut, 
fig. 12, as the cavity projects upwards for 1}'' on each side of a median ridge, through 
which the section is made. ‘The cerebral hemispheres must have a remarkable deve- 
lopment in this direction, projecting considerably beyond the cerebellum, which, as its 
limits appear to be indicated by a rather obscure nearly horizontal ridge, would have a 
small proportionate development. On the other hand, the magnitude of the apertures 
for the principal nerves, as well as the canal for the medulla oblongata, shows that these 
were of great relative size. The greatest transverse diameter of the cerebral cavity is 15”. 
The planes and angles formed by the different parts of the wall of the cranial cavity 
are very remarkable. The lowest part is at the junction of the basioccipital with the 
basisphenoid. Behind this the basioccipital rises upwards at an angle of 45° from a 
horizontal line drawn from one end of the cranium to the other, so that the long and 
capacious canal in the occipital bone, leading to the foramen magnum, rises above the 
level of the brain-cavity. The basisphenoid is inclined slightly upwards towards its 
junction with the presphenoid. The concave anterior wall of the cavity formed by the 
united presphenoid and ethmoid is nearly vertical in its general direction. The anterior 
half of the roof, formed by the frontal, is straight (somewhat depressed in the young 
skull), and directed upwards and backwards at an angle of 45° to the horizontal line. 
The hinder part of the roof, formed by the occipital, arches downwards and backwards, 
* Cat. Osteol. Ser. Mus. Roy. Coll. Surg. vol, ii. p. 442, 1853. 
