Page:Encyclopædia Britannica, Ninth Edition, v. 15.djvu/417

CETACEA.] tained by members of this important group of mammals, though largely increased of late years, is still imperfect. Formerly they were all divided into Right Whales (Bal&na) and Rorquals or Fin- }iii}cs(Balsenoptcra), the latter distinguished by their smaller heads, elongated and slender form, free cervical vertebra, tetradactylous man us, and the presence of very conspicuous longitudinal furrows or folds in the skin of the throat and chest, and of a small adipose dorsal fin. Recent discoveries have, however, brought to light several forms holding a somewhat intermediate position, and pre senting combinations of characters not found in either of the larger known sections. According to our present knowledge the group is naturally divided into five very distinct genera. As these will be more fully described in the article WHALE, it will be sufficient at present to indicate their principal characteristics. Balasna. Skin of throat smooth, not furrowed. No dorsal fin. Cervical vertebrse united into a single mass. Pectoral limb short, broad, and pentadactylous. Head very large. Baleen very long and narrow, highly elastic and black. Scapula high, with a distinct coracoid and coronoid process. This genus contains the well-known Greenland Right Whale (B. mysticetus) of the Arctic seas, the whale bone and oil of which are so much valued in commerce, and also other whales, distinguished from this by having heads somewhat smaller in proportion to the body, with shorter baleen, and a larger number of vertebrae. These inhabit the temperate seas of both northern and southern hemispheres, and have been divided by zoologists into several species in accordance with their geographical distribution, B. biscaycnsis of the North Atlantic, B. japonica of the North Pacific, B. australis of the South Atlantic, and B. nntipodarum and novte-zclandise of the South Pacific ; but the differential characters by which they have been separated external as well as anatomical are so slight and so liable to individual varia tion that it is not improbable that when they are better known they will all come to be regarded as forming but a single species. Xeohdaena. Known chiefly at present by the characters of the skeleton and baleen, which are very different from those of all other whales, but said to combine absence of plications of the throat with the presence of a dorsal fin. The cervical vertebrae are united. The manus small, narrow, and tetradactylous, wanting the pollex. The ribs remarkably expanded and flattened. The scapula very low and broad, with completely developed acromion and coracoid processes. Baleen very long, slender, elastic, and white. A single at present very rare species, N. marginala, from the Australian and New Zealand seas, is the smallest of the Whalebone Whales, being not more than 20 feet in length. Kachianectcs. This combines the small head, elongated form, and narrow pectoral fin of Balsenoptera with the smooth skin of the throat and absence of the dorsal fin of Bal&na. The baleen is the shortest and coarsest of any of the group. Its osteology is im perfectly known. One species, E. glaucus, the Grey Whale of the North Pacific. Megaptera. Head of moderate size. Baleen plates short and broad. Cervical vertebrae free. Scapula with acromion and coracoid process absent or rudimentary. Skin of throat plicated. Dorsal fin low. Pectoral limb tetradactylous, very long and narrow, attaining about one-fourth of the length of the entire animal, the metacarpus and phalanges being greatly developed, and the latter very numerous. Animals of this genus, called " Humpbacks" by the whalers, are found in almost all seas. They have been divided into many species, but no satisfactory characters have yet been pointed out by which these can be distinguished from one another. Balsenoptera. Head small and flat, and pointed in front. Body long and slender. Skin of throat plicated. A small falcate dorsal fin. Baleen short and coarse. Cervical vertebra free. Scapula low and broad, with a large acromion and coracoid process. Pectoral limb tetradactylous, small, narrow, and pointed. This genus con tains the various species of Rorquals, Fin-whales, Fin-backs, Finners, or Razor-backs, as they are variously called, some of which are found in almost every sea. Among them are the most gigantic of all animals, B. sibbaldii, which attains the length of 80 feet, and the small B. rostrata, which does not exceed 30. There are certainly four quite distinct modifications of this genus, represented by the two just mentioned, and by B. musculus and B. borealis, all inhabitants of British seas, but the question whether almost identical forms found in the Southern and Pacific Oceans are to be regarded as specifically identical or as distinct awaits the result of future researches. SUBORDER ARCIIJEOCETI. This group is formed to include certain extinct Cetaceans, which are at present only known by more or less fragmentary portions of their skeleton and teeth, and whose position and affinities are therefore still subject to doubt. In the anterior part of both jaws the teeth are simple, conical, or slightly compressed, and sharp-pointed. The first three in the upper jaw are distinctly implanted in the premaxillary bone, and so may be reckoned as incisors. The tooth which succeeds, or the canine, is also simple and conical, but it does not exceed the others 395 in size. This is followed by five teeth with two distinct roots, and compressed, pointed crowns, with denticulated cutting edges. The dentition is therefore i f, c {, p and m = 36, resembling that of some Seals. 1 General form of the skull elongated and much depressed. Brain cavity very small, and the skull between it and the orbits elongated and narrow. Temporal fossaj very large. A strong sagittal crest. Rostrum long and narrow, differing from that of other Cetaceans in the large extent to which the premaxillne form the sides of the anterior extremity. Nasal bones elongated, flat, and narrow, the opening of the anterior nares being over the middle of the elongated compressed rostrum. All the cervical vertebra free. The characters of the dorsal vertebra, and mode of articulation of the ribs, appear to have resembled those of Platanista rather than Balssna, Plnjsctcr, or Dclphinus. Lumbar vertebrae with elongated bodies. Characters of the limbs not known with certainty. 2 All the known fossil remains belonging to the animals of this group may be referred, provisionally at least, to the genus Zeuglodon, so named because the first section of a molar tooth examined was taken from the base of the crown, where it was beginning to divide into the two roots, and looked like two single teeth " linked or yoked together." This name was substituted by Owen for the earlier one Basilosaurus of Harlan, with the consent of that author, on the mammalian nature of the animal being demonstrated. 3 The latter name is, however, still generally retained by American zoologists. The remains have hitherto been found chiefly in the Eocene for mations of the States of Alabama, Louisiana, Mississippi, and Arkansas, and have been assigned to several species. A portion of a skull is recorded from the Barton Clay (Eocene) of Hampshire, England. SUBORDER ODONTOCETI, the DELPHINOIDEA, or Toothed Whales. Calcined teeth always present after birth ; generally numerous, but sometimes a very limited number (in a few cases none) are functionally developed. No baleen. Upper surface of the skull more or less asymmetrical. Nasal bones in the form of nodules or flattened plates, applied closely to the frontals, and not forming any part of the roof to the uarial passage, which is directed upwards and backwards. Olfactory organ rudimentary or absent. Hinder end of the maxilla expanded and covering the greater part of the orbital plate of the frontal bone. Lacrymal bone either inseparable from the jugal, or, when distinct, very large, and forming part of" the roof of the orbit. Tympanic bone not ankylosed with the periotic, which is usually only attached to the rest of the skull by ligament. Kami of mandible nearly straight, much expanded in height posteriorly, with a wide funnel-shaped aperture to the dental canal, and coming in contact in front by a flat surface of variable length, but always constituting a true symphysis. Several of the anterior ribs with well-developed capitular processes, which articu late with the bodies of the vertebra. Sternum almost always com posed of several pieces, placed one behind the other, with which several pairs of ribs are always connected by the intervention of well-developed cartilaginous or ossified sternal ribs. External respiratory aperture single, the two nostrils uniting before they reach the surface, usually in the form of a transverse subcrescentie valvular aperture, situated on the top of the head. Maims always pentadactylous, though the first and fifth digits are usually very little developed. No caecum, except in Platanista. Family PHYSETERID.E. No functional teeth in the upper jaw. Mandibular teeth various, often much reduced in number. Bones of the cranium raised so as to form an elevated prominence or crest behind the nares. Pterygoid bones thick, produced backwards, meeting in the middle line, and not involuted to form the outer wall of the post-palatine air-sinuses, but simply hollowed on their outer side. Transverse processes of the arches of the dorsal vertebra, to which the tubercles of the ribs are attached, ceasing abruptly near the end of the series, and replaced by processes on the body at a much lower level, and not on a line, or serially homologous with them, but serially homologous anteriorly with the heads of the ribs, and posteriorly with the transverse processes of the lumbar vertebra;. (In some genera, as Physetcr, the two processes, upper and lower on each side, are both present and well developed in the same vertebra in the region of transition. In others, as Ziphius and Berardius, they are not both developed on any single vertebra.) Costal cartilages not ossified. Subfamily Physeterinee. Numerous teeth in the mandible, which are not set in distinct bony alveoli, but in a long groove di ts is 1 An appearance in one specimen lias been described by C. G. Cams as in eating a vertical succession of the teeth, but the evidence upon which this rest* ... by no means satisfactory, and appears to admit of another explanation. _ 2 A mutilated humerus of Zeuglodon cetoides has given rise to many conjectures, appealing to some anatomists to indicate Seal-like freedom of motion at the elbow- joint, while to others its characters appear to be truly Cetacean.

3 See Trans. Geol. Soc. Land., ser. ii., vol. vi. p. 67.