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 fore-limb 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 



