Skull broad and depressed. Premaxillæ strongly concave in front of nares. Vertebral formula: cervicals 7, dorsals 11, lumbars 12–14, caudals 28–29. Total, 58 or 59. Habitat: North Atlantic Ocean.
BOTTLENOSE PORPOISE
Tursiops truncatus (Mont.)
Head produced in the form of a beak. Strong teeth in both jaws. A well-developed dorsal fin.
The color is dark gray on the head, back and sides, and the throat, breast and belly are white. Average length, 8 feet; greatest length, 12 feet.
Rostrum tapering. Palate not grooved. Symphysis of mandible short. Forty to 50 teeth. Vertebral formula: cervicals 7, dorsals 13, lumbars 17, caudals 27. Total, 64. Habitat: North Atlantic Ocean.
III. THE SKELETON OF THE CETACEA
The skeletons of whales and porpoises are so frequently preserved in museums that, for the benefit of those who wish to understand more fully the Cetacea, a brief general description of the osteology is given below. Unfortunately, however, it is impossible to present the subject except in semi-technical language.
The bones of the Cetacea are comparatively light and fragile, the hard, shell-like exterior being thin and the interior filled with spongy “cancellous tissue” which is considerably impregnated with oil. In structure they are exactly opposite to those of the Sirenia (the aquatic mammalian order including the sea cows, or manatees, and the dugongs), which have very heavy solid bones of almost flinty hardness. Cetacean bones are easily affected by weather, and if exposed to the sun, rain and wind for a comparatively short time the hard exterior becomes white and chalk-like.
The whale’s skeleton is highly modified in adaptation to an aquatic existence and is very distinctive of the cetacean order. In a general view it is seen to be greatly elongated, the skull is pointed, the fore-limbs are short and flat and the hind-limbs are represented by nodules of bone; all these accompany a fish-like body which offers little resistance to its passage through the water.
The skull is perhaps more greatly modified than any other portion of the skeleton, and if a trained anatomist who had not studied the Cetacea were to examine a whale’s skull, he would probably be at a loss to identify correctly its parts. The brain case is small and rounded, the eyes are situated far back and the facial portion greatly elongated. The back of the brain case is formed by an extraordinarily developed supra-occipital bone which extends forward and upward to meet the frontal, entirely excluding the parietals from the summit of the skull. The nostrils have rotated backward and upward and are almost vertical instead of horizontal as in other mammals; thus the nasal bones are greatly reduced in size.