ME. W. H. FLO WEE ON THE OSTEOLOGY OE THE SPEEM-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 

 aff"ects the entire wall of the great supracranial basin, as seen in the upper view of the 

 young skull (PI. LVII. fig. 1). 



As the indi\'idual 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 diflerent 

 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 examined. 



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 PI. 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 13". 



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. Mua. Eoy. Coll. Surg. vol. ii. p. 442, 1853. 



