in fact (fig. 1). The supra-occipital bone rises upwards
and forwards from the foramen magnum, to meet the frontals at the
vertex, completely excluding the parietals from the upper region; and
the frontals are expanded laterally to form the roof of the orbits.
The nasal aperture opens upwards, and has in front of it a more or
less horizontally prolonged beak, formed of the maxillae, premaxillae,
vomer, and mesethmoid cartilage, extending forwards to form the upper
jaw or roof of the mouth.

There are no clavicles. The humerus is freely movable on the scapula
at the shoulder-joint, but beyond this the articulations of the limb
are imperfect; the flattened ends of the bones coming in contact, with
fibrous tissue interposed, allowing of scarcely any motion. The radius
and ulna are distinct, and about equally developed, and much
flattened, as are all the bones of the flippers. There are four, or
more commonly five, digits, and the number of the phalanges of the
second and third always exceeds the normal number in mammals,
sometimes considerably; they present the exceptional character of
having epiphyses at both ends. The pelvis is represented by a pair of
small rod-like bones placed longitudinally, suspended below and at
some distance from the vertebral column at the commencement of the
tail. In some species, to the outer surface of these are fixed other
small bones or cartilages, the rudiments of the hind-limb.

[Illustration: FIG. 1.--A Section of the Skull of a Black-Fish
(_Globicephalus melas_).

PMx, Premaxilla.
Mx, Maxilla.
ME, Ossified portion of the mesethmoid.
an, Nostrils.
Na, Nasal.
IP, Inter-parietal.
Fr, Frontal.
Pa, Parietal.
SO, Supra-occipital.
ExO, Ex-occipital.
BO, Basi-occipital.
Sq, Squamosal.
Per, Periotic.
AS, Alisphenoid.
PS, Presphenoid.
Pt, Pterygoid.
pn, Posterior nares.
Pl, Palatine.
Vo, Vomer.
s, Symphysis of lower jaw.
id, Inferior dental canal.
cp, Coronoid process of lower jaw.
cd, Condyle.
a, Angle.
sh, Stylo-hyal.
bh, Basi-hyal.
th, Thyro-hyal.]

Teeth are generally present, but exceedingly variable in number. In
existing species, they are of simple, uniform character, with conical
or compressed crowns and single roots, and are never preceded by
milk-teeth. In the whalebone whales teeth are absent (except in the