Page:Mammalia (Beddard).djvu/359



Aquatic Mammalia of fish-like form; tail expanded into horizontal flukes; a fatty dorsal "fin" present in most species; anterior limbs converted into fin-like paddles; posterior limbs only represented by skeletal rudiments. Hairy covering reduced to a few isolated hairs in the neighbourhood of the muzzle. Nostrils represented by the single or double blow-hole, nearly always situated far back upon the skull. Bones of loose texture and much impregnated with oil. The skull has a greatly-developed facial portion; supra-occipital bones meeting the frontal by overgrowing, or growing in between the parietals; bones surrounding the organ of hearing loosely attached to the skull, the tympanics of peculiar cowrie-shell form. Coronoid process of mandible absent, or very feebly developed. Teeth, when present, few or numerous, always of simple conical form, with at most traces of additional cusps (Inia); if absent their place taken by whalebone. Cervical vertebrae of short antero-posterior diameter, often more or less completely welded together into a single mass. Articulations between dorsal and other vertebrae feeble. Scapula peculiarly flattened; acromion strongly developed as a rule, but arising from a slightly-marked spine; coracoid process generally strongly developed. Phalanges of digits always more numerous than in other mammals. Clavicles absent. Stomach complex, consisting of at least four and often more chambers. Lungs simple and non-lobulated. Diaphragm obliquely set and very