4 CETACEANS. 
commonly known as “whalebone,” the nature of which will be explained later on. 
Even in this group, however, there are rudiments of teeth deeply buried in the gums 
of the young; and the structure of these rudiments is such as to indicate the origin 
of at least that group of Cetaceans from mammals furnished with teeth of a 
complex type. It is further inferred by Dr. Ktikenthal that these rudimentary 
teeth correspond with those of the permanent set in other mammals. 
In conformity with the absence of any external indications of a 
neck, the vertebree in that region of the backbone of Cetaceans are 
abnormally shortened, so that even in the largest species this part of the column 
may not much exceed a foot in length. This shortening of the neck is, however, 
not accomplished by any reduction in the number of the vertebree from the normal 
seven, but by the shortening of the body of each of these vertebrze until it assumes 
the form of a broad, thin plate. The necks of a giraffe and a whale present, 
therefore, the extremes in the modifications assumed by their constituent vertebre ; 
these joints undergoing the maximum degree of elongation in the one, and of 
abbreviation in the other. In many Cetaceans the whole or a certain number of 
the vertebrae of the neck are welded together into one solid mass. In the hinder 
portion of the backbone the region of the tail is only distinguished from that of 
the trunk by the vertebrz (as shown in our figure of the skeleton of the Greenland 
whale) carrying chevron-bones affixed to their under-surfaces; there being no 
Neck. 
mass of united vertebrae, corresponding to the sacrum of other mammals. 
The skeleton of the fore-limbs exhibits all the segments 
characterising those of terrestrial mammals, although some of these 
are much modified. There are no eollar-bones (clavicles) ; but the shoulder-blades, 
or scapulze, are very large, and are much elongated in the antero-posterior direction. 
The humerus, or bone of the upper arm, although much shorter than usual, has a 
free movement at its articulation with the shoulder-blade; but its Junction with 
the two bones of the fore-arm, like all the jomts lower down in the limb, admits of 
scarcely any motion. Indeed, in all these joints the bones articulate by flattened 
surfaces closely applied to one another, and are bound together by fibrous tissue. 
The bones of the fore-arm (radius and ulna) are elongated and flattened, and lie 
nearly parallel, one in front of the other. The number of digits in the flippers is 
usually five, although occasionally reduced to four; and in the second and third of 
these there are always more than the ordinary three joimts below the metacarpus. 
The only rudiments of the hind-limbs are a few small bones beneath the sacral 
region of the backbone representing part of the pelvis, and occasionally part of the 
limb itself (f, and p. in the figure on p. 2). 
In accordance with the position of the nostrils at its summit, the 
skull departs considerably from the ordinary type. It will suffice to 
state here that the supraoccipital bone extends forward to join the frontals, and 
thus excludes the parietal bones from taking any share in the formation of the roof 
of the middle line of the skull; while in front of the opening for the nostrils there 
is a more or less prolonged rostrum. 
In regard to the soft parts, it may be mentioned that the stomach 
is always complex; and that the female has two teats, placed far 
back on the abdomen. In order to enable these animals to swim with their mouths 
Limbs. 
SkulL 
Soft Parts. 
