318 MR. W. H. FLOWER ON THE OSTEOLOGY OF THE SPERM-WHALE. 
ends abruptly in a narrow bifid extremity on a level with the posterior margin of this 
passage ; the right continues onwards, and, passing the blow-hole, expands into a thin 
broad plate, applied to the anterior surface of the frontal, and reaching to within 6" 
of the summit of the crest. 
On the left side, corresponding to this plate, overlying the frontal, and resting below 
on the top of the ethmoid, is a large, flat, very thin, loose lamina of bone (n). Its lower 
edge is thicker and rounded; but it terminates above by delicate irregular digitations. 
This measures 14” in breadth, and rather more in height; but a considerable part 
appears to be wanting from its upper edge in the adult specimen, having probably been 
lost in maceration, or perhaps never completely ossitied. It is more perfect in the young 
skull, and partially united to the frontal (see Pl. LVII. fig. 1). This I take to be the 
left nasal bone, as it corresponds in situation and relations with that bone in the 
Hyperoodon, although, in common with the other bones of the crest, it is excessively 
flattened out. 
In none of the skulls examined could any trace of a right nasal bone be seen. Its 
development appears to be interfered with by the ascending plate of the premaxillary ; 
or it is possible that it is concealed beneath this. In the foetal skull in the Museum of 
the College of Surgeons, described by Owen and Huxley, the left nasal is absent; pro- 
bably it was not ossified at this early age. 
In front of the blow-holes the upper surface of the skull is comparatively flat, 
although still rising in the greater part of its extent from the centre towards the sides. 
This region is formed by the premaxillaries, in the shape of a pair of long narrow bands 
of varying width, with very sharp edges overhanging the median vomerine groove, but 
mainly by the greatly developed rostral portion of the maxillaries. These bones are very 
massive, and expand in width in front of the deeply marked antorbital notch (aon). 
Their flat upper surface is formed of a very thin plate of bone of remarkably dense and 
brittle texture. Their internal structure is cancellous, the large distinct cells, almost 
like those of a honeycomb, being filled in the natural state with oil. 
The infraorbital foramen (7 f') is represented by a fissure 10” in length, and 2” in 
breadth, placed between the blow-hole and the antorbital notch, but nearer the latter. 
This gives passage to the great branches of the fifth nerve destined to supply the enor- 
mous upper lip and face. 
In the right premaxillary, 15” in front of the blow-hole, is an oval fossa, 3’ in 
length, leading into a canal which runs outwards, and communicates with that leading 
to the infraorbital foramen. There is no corresponding opening on the left side. 
Lateral surface of the Skull (Pl. LY.).—The temporal fossa is very small, though 
scarcely so much reduced as in Hyperoodon. It is especially compressed from before 
backwards, lying deeply between the great projecting masses formed by the squamosal 
behind and the orbital process of the frontal in front. Above, it has not any distinct 
limiting ridge as in /yperoodon and most Dolphins, but passes almost insensibly on to 
