7 o6 



MAMMALIA. 



The cervical vertebrae are thin and more or less fused. 

 There is no union of vertebrae to form a sacrum, for the 

 hind-limbs are at most very rudimentary. Under the caudal 

 vertebrae there are wedge-shaped chevron bones. 



The brain-case is almost spherical ; the supra-occipital 

 meets the frontals and shuts out the parietals from the roof 

 of the skull ; the frontals arch over the orbit ; the snout or 

 rostrum of the skull is composed of premaxillae, maxillae, 

 and vomer, and of the mesethmoid 

 cartilage. 



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 re- 

 sulted from a splitting of more com- 

 plex cusped teeth. No clavicles are" de- 

 veloped. Excepting the humerus, the 

 bones of the fore-limb are stiffly jointed 

 and flattened. The carpals are fixed 

 in a fibrous matrix, tend to be rudi- 

 mentary, and are often unossified. 

 There are four or five digits, of which 

 the second and third have more than the 

 usual number of phalanges, a peculiarity 

 possibly due to a duplication and sepa- 

 ration of epiphyses. The pelvis may 

 exhibit two rudimentary ischia, 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 



FIG. 259. Fore- 

 limb of Whale (Me- 



gaptera longiviand]. 

 (After STRUTHERS.) 



