226 CETACEA 
The bones generally are spongy in texture, the cavities being 
filled with oil. In the vertebral column the cervical region is 
remarkably short and immobile, and the vertebre, originally 
always seven in number, are in many species more or less fused 
together into a solid mass. The odontoid process of the axis, when 
that bone is free, is usually very obtuse, or even obsolete. None 
of the vertebr are united together to form a sacrum. The lumbar 
and caudal vertebre are numerous and large, and, as their arches 
are not connected by any articular processes (zygapophyses), they 
are capable of a very free motion in all directions. The epiphyses 
at the ends of the vertebral bodies are very distinct flattened disks, 
not uniting until after the animal has attained its full dimensions.* 
There are largely developed chevron bones, the presence of which 
indicates the distinction between the caudal and lumbar vertebre. 
The skull (Fig. 75) is modified in a very peculiar manner. The 
brain-case is short, broad, and high, in fact almost spherical. The 
supraoccipital bone rises upwards and forwards from the foramen 
magnum, to meet the frontals at the vertex, thus completely 
excluding the parietals from the upper region of the cranium. The 
frontals are expanded laterally to form the roof of the orbits. The 
anterior narial aperture opens upwards, and has in front of it a 
more or less horizontally prolonged rostrum, formed of the maxillz, 
premaxille, 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 each other, with fibrous tissue interposed, allowing of 
scarcely any motion. The radius and ulna are distinct, about 
equally developed, and much flattened, as are also all the bones 
of the manus. There are four, or more commonly five digits, and 
the number of the phalanges of the second and third digits always 
exceeds the normal number in mammals, sometimes very con- 
siderably (hyperphalangism) ; they present the exceptional character 
of having epiphyses at both ends.2_ The pelvis is represented by a 
pair of small styliform bones placed longitudinally, suspended below 
and at some distance from the vertebral column at the commence- 
ment of the caudal region. These appear to represent the ischia, 
as the crura of the corpora cavernosa are attached to them. In 
some species, to the outer surface of these are fixed other small 
bones or cartilages, the rudiments of the hind limb. 
1 This is an important distinction from the Sirenia, but a character common 
to nearly all other mammals. It is doubtful whether there is any foundation 
for the statement that these epiphyses remain ununited for an exceptionally long 
period in the Cetacea. 
2 A character repeated in some of the Seals, 
