768 MAMMALIA 
and vomer, and of the mesethmoid cartilage. The periotic 
in whales is an exceedingly dense bone, and is of interest 
because it is the only part of the skeleton found at great 
depths on the floor of the ocean, and is often preserved as 
a fossil. 
There are at least rudiments of two sets of teeth, as 
in other Mammals, but in baleen whales only the teeth of 
the milk set are calcified, and they come withal to nothing, 
being to some extent replaced by the horny baleen-plates 
developed on the palate. In toothed whales the two sets 
are said by Kiikenthal to fuse, but the usual interpretation 
is that the functional teeth belong to the milk set. It 
is possible that the simple, homodont, conical teeth of 
Odontoceti have resulted from a splitting of more complex 
cusped teeth. No clavicles are developed. The bones of 
the forelimb are flattened, and, except at the shoulder, 
articular surfaces are not developed, so that the limbs form 
stiff paddles. The carpals are fixed in a fibrous matrix, 
tend to be rudimentary, and are often unossified. They 
cannot be readily compared with the members of the 
typical mammalian carpus. In the absence of true joints, 
a slight flexibility is given by the absence of ossification. 
There are four or five nailless digits, of which the second 
and third, and sometimes the first, may have more than 
the usual number of phalanges (see Fig. 413), a peculiarity 
possibly due to a duplication and separation of epiphyses. 
The pelvis may exhibit a rudimentary ischium, with small 
vestiges of femur and tibia. 
The rounded brain is relatively large, with well-convoluted 
cerebral hemispheres. 
As to the alimentary system,—salivary glands are: rudi- 
mentary or absent, the stomach is chambered, the intestine 
has rarely a caecum, the liver is but slightly lobed, there is 
no gall-bladder. 
The heart is often cleft between the ventricles. Both 
arteries and veins tend to form retia mirabilia. 
The larynx is elongated, so that it meets the posterior 
nares, and forms a continuous canal, down which air passes 
from nostrils to. lungs. The inspiration and expiration 
occur at longer intervals than in terrestrial mammals. The 
water-vapour expelled along with the air from the lungs 
