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 vertebra?, 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 vertebrae are united together to form a sacrum. The lumbar 

 and caudal vertebras 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. 1 

 There are largely developed chevron bones, the presence of which 

 indicates the distinction between the caudal and lumbar vertebrae. 



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 maxilla?, 

 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 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. 



