MR. W. H. FLOWER ON THE OSTEOLOGY OF THE SPERM-WHALE. 517 
outwards and forwards. In the young skull the division of this canal into three 
branches takes place close to the cranial cavity. ‘The first represents the sphenoidal 
fissure ; the second and third, which perforate the alisphenoid, represent the foramen 
rotundum and foramen ovale respectively. 
4. Immediately behind and rather lower than the last is a nearly circular and much 
smaller foramen, perforating obliquely the outer side of the basisphenoid near its union 
with the alisphenoid. This appears to be the carotid canal. 
5. ‘The remaining nerve-openings are collected into one, large, elongated, funnel-shaped 
canal, leading outwards and downwards from the side of the lowest part of the brain- 
cavity. At the bottom of this canal, and 14” distant from its commencement, is 
placed the organ of hearing. 
Upper surface of the Skull—The general shape of this region has been already 
described. We may commence a more special description by taking the narial apertures 
as central points. The left, which extends close to the median line of the cranium, 
is nearly circular in outline above, having a diameter of about a foot, and is directed 
slightly forwards and to the left side. It contracts somewhat, and is more oval in form, 
below, with the long diameter fore and aft. At its narrowest part it is 77” by 113”. 
Its upper margin is formed by the vomer on the inner side, the premaxillary in front 
and the outer side, the maxillary behind this on the outer side, and posteriorly by a 
rough spongy mass growing out from the left side of the ethmoid, forming a kind of 
operculum projecting over the narial opening (Pl. LVI. fig. 1,¢). In the young specimen 
this singular mass is not fully ossified, and is therefore a much less conspicuous feature 
in the skull (Pl. LVI. fig. 2). Lower down, the vomer passes all round the back and 
nearly as far as the middle of the outer side of the passage, while the pterygoid forms 
the remainder of its inferior boundary. In the anterior and outer wall, a small slip of 
the palatal appears. 
The right blow-hole is placed nearer the hinder part of the skull than the left. It 
is an irregularly circular canal, with an average diameter of 3”, directed upwards and 
backwards. The septum which divides it from the left is 3” wide at the narrowest 
part. 
The great semicircular wall which rises up behind the narial apertures is formed by the 
extremely compressed hinder portion of the maxillaries and premaxillaries, the frontals 
and the nasals, the whole being backed up behind and on each side by the supra- 
occipital, and perhaps containing some portion of the parietals concealed within. The 
maxillaries form the greatly thickened and sloping lateral edges of the crest. They rise 
to the highest part of it, but do not meet in the middle line by the space of more than a 
foot. Their inner edge is extremely thin. They present no special asymmetry in develop- 
ment. On the other hand, the premaxillaries of the two sides differ greatly: passing 
backwards along from the upper surface of the rostrum, where they lie on each side of 
the median vomerine groove, the left, turned out of its course by the great blow-hole, 
VOL. VI.—PART VI. 2Y 
