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CETACEA

until they are worn, without enamel. Upper surface of the skull concave; its posterior and lateral edges raised into a very high and greatly compressed semicircular crest or wall (fig. 2). Zygomatic processes of jugal bones thick and massive. Muzzle greatly elongated, broad at the base, and gradually tapering to the apex. Lower jaw exceedingly long and narrow, the symphysis being more than half the length. Vertebrae: C 7, D 11, L 8, Ca 24; total 50. Atlas, or first vertebra, free; all the other cervical vertebrae united by their bodies and spines into a single mass. Eleventh pair of ribs rudimentary. Head about one-third the length of the body; very massive, high and truncated, and rather compressed in front; owing its huge size and form mainly to the accumulation of a mass of fatty tissue filling the large hollow on the upper surface of the skull and overlying the long muzzle. The single blow-hole is longitudinal, slightly S-shaped, and placed at the upper and anterior extremity of the head to the left side of the middle line. The opening of the mouth is on the under side of the head, considerably behind the end of the snout. Flippers short, broad and truncated. Dorsal fin represented by a low protuberance. See Sperm-Whale.

EB1911 Cetacea - Fig. 2.—Skull of Sperm-Whale.jpg
Fig. 2.—Skull of Sperm-Whale (Physeter macrocephalus).

In the lesser or pigmy sperm-whale (Cogia breviceps) there may be a pair of rudimentary teeth in the upper jaw, while on each side of the lower jaw there are from 9 to 12 rather long, slender, pointed and curved teeth, with a coating of enamel. Upper surface of the skull concave, with thick, raised, posterior and lateral margins, massive and rounded at their anterior terminations above the orbits. Muzzle not longer than the cranial position of the skull, broad at the base, and rapidly tapering to the apex. Zygomatic process of the jugal rod-like. Lower jaw with symphysis less than half its length. Vertebrae: C 7, D 13 or 14, L and Ca 30; total 50 or 51. All the cervical vertebrae united by their bodies and arches. The head is about one-sixth of the length of the body, and obtusely pointed in front; the mouth small and placed far below the apex of the snout; the blow-hole crescentic, and placed obliquely on the crown of the head in advance of the eyes and to the left of the middle line; while the flippers are bluntly sickle-shaped, and the back-fin triangular. This species attains a length of from 9 to 13 ft.

EB1911 Cetacea - Fig. 3.—Bottle-nose (Hyperoödon rostratus).jpg
Fig. 3.—Bottle-nose (Hyperoödon rostratus). From a specimen taken off the coast of Scotland, 1882.

A second subfamily is represented by the bottle-noses and beaked whales, and known as the Ziphiinae. In this group the lower teeth are rudimentary and concealed in the gum, except one, or rarely two, pairs which may be largely developed, especially in the male. There is a distinct lacrymal bone. Externally the mouth is produced into a slender rostrum or beak, from above which the rounded eminence formed by a cushion of fat resting on the cranium in front of the blow-hole rises somewhat abruptly. The blow-hole is single, crescentic and median, as in the Delphinidae. Flippers small, ovate, with five digits moderately well developed. A small obtuse dorsal fin situated considerably behind the middle of the back. Longitudinal grooves on each side of the skin of the throat, diverging posteriorly, and nearly meeting in front. In external characters and habits the whales of this group closely resemble each other. They appear to be almost exclusively feeders on cuttle-fishes, and occur either singly, in pairs, or in small herds. By their dental and osteological characters they are easily separated into four genera.

In the first of these, Hyperoödon, or bottle-nose, there is a small conical pointed tooth at the apex of each half of the lower jaw, concealed by the gum during life. Skull with the upper ends of the premaxillae rising suddenly behind the nostrils to the vertex and expanded laterally, their outer edges curving backwards and their anterior surfaces arching forwards and overhanging the nostrils; the right larger than the left. Nasal bones lying in the hollow between the upper extremities of the premaxillae, strongly concave in the middle line and in front; their outer edges, especially that of the right, expanded over the front of the inner border of the maxilla. Very high longitudinal crests on the maxillae at the base of the beak, extending backwards almost to the nostrils, approaching each other in the middle line above; sometimes compressed and sometimes so massive that their inner edges come almost in contact. Preorbital notch distinct, and mesethmoid cartilage slightly ossified. Vertebrae: C 7, D 9, L 10, Ca 19; total 45. All the cervical vertebrae united. Upper surface of the head in front of the blow-hole very prominent and rounded, rising abruptly from above the small, distinct snout. Two species are known. See Bottle-nose Whale.

The typical representative of the beaked whales is Ziphius cuvieri, in which there is a single conical tooth of moderate size on each side close to the anterior extremity of the lower jaw, directed forwards and upwards. Skull with the premaxillae immediately in front and at the sides of the nostrils expanded, hollowed, with elevated lateral margins, the posterior ends rising to the vertex and curving forwards, the right being considerably more developed than the left. The conjoint nasals form a pronounced symmetrical eminence at the top of the skull, projecting forwards over the nostrils, flat above, prominent and rounded in the middle line in front, and separated by a notch on each side from the premaxillae. Preorbital notch not distinct. Rostrum (seen from above) triangular, tapering from the base to the apex; upper and outer edges of maxillae at base of rostrum raised into low roughened tuberosities. Mesethmoid cartilage densely ossified in adult age, and coalescing with the surrounding bones of the rostrum. Vertebrae: C 7, D 10, L 10, Ca 22; total 49. The three anterior cervical vertebrae united, the rest free.

EB1911 Cetacea - Fig. 4.—Sowerby’s Beaked Whale (Mesoplodon bidens).jpg
Fig. 4.—Sowerby’s Beaked Whale (Mesoplodon bidens).

In the numerous species of the allied genus Mesoplodon there is a much-compressed and pointed tooth in each half of the lower jaw, variously situated, but generally at some distance behind the apex; its point directed upwards, and often somewhat backwards, occasionally developed to a great size. In the skull the region round the nostrils is as in Hyperoödon, except that the nasals are narrow and more sunk between the upper ends of the premaxillae; like those of Hyperoödon, they are concave in the middle line in front and above. No maxillary tuberosities. Preorbital notch not very distinct. Rostrum long and narrow. Mesethmoid in the adult ossified in its entire length, and coalescing with the surrounding bones. Vertebrae: C 7, D 10, L 10 or 11, Ca 19 or 20; total 46 to 48. Two or three anterior cervicals united, the rest usually free.

EB1911 Cetacea - Fig. 5.—Skull of a Beaked Whale (Mesoplodon densirostris).jpg
Fig. 5.—Skull of a Beaked Whale (Mesoplodon densirostris).

Though varying in form, the lower teeth of the different members of this genus agree in their essential structure, having a small and pointed enamel-covered crown, composed of dentine, which, instead of surmounting a root of the ordinary character, is raised upon a solid mass of osteo-dentine, the continuous growth of which greatly alters the form and general appearance of the tooth as age advances, as in the case of M. layardi, where the long, narrow, flat, strap-like teeth, curving inwards at their extremities, meet over the rostrum, and interfere with the movements of the jaw. In one species (M. grayi) a row of minute, conical, pointed teeth, like those of ordinary Dolphins, 17 to 19 in number, is present even in the adults, on each side of the middle part of the upper jaw, but embedded by their roots only in the gum, and not in bony sockets. This, with the frequent presence of rudimentary teeth in other species of this genus, indicates that the beaked whales are derived from ancestral forms with teeth of normal character in both jaws. The species are distributed in both northern and southern hemispheres, but most frequent in the latter. Among them are M. bidens, M. europaeas, M. densirostris, M. layardi, M. grayi and M. hectori; but there is still much to be learned with regard to their characters