Ep, epiglottis; vc, vocal cord; s, sac; c, cartilage; gl, gland; tr, trachea. The arrows show direction of air-currents in ingress and egress.
SKELETON OF SPERM WHALE. (After Flower.)
s, Spermaceti Cavity; n, Nasal Passage, in dotted line; b, Blowhole.
Cetacea have been a troublesome group to unravel, being ocean-dwellers, and many of them huge brutes. To study them in the live state has been difficult, and their carcases when captured or stranded on shore are as unmanageable for purposes of examination. As to their classification the two sub-orders—Denticete, Toothed Whales, and Mysticete, Whalebone Whales—are universally accepted. As regards the families, the main groups are tolerably well agreed upon, though differently named by authorities. Among the sub-families, the genera and the species, there is less unanimity. The grouping of the living forms proposed by Professor Flower is in Great Britain more frequently adopted, while MM. Gervais and Van Beneden, in their great work on “Osteographie des Cétacés,” have collated the living and fossil forms. Some species and genera of Whales are restricted within given areas, as are the Seals, but of the habitat of many others in truth so little is known that no defined limit can be assigned. The great majority are migratory; some are gregarious, others more solitary in disposition. A few are quite fluviatile; but most are found in the high seas. Following the above primary divisions, we give precedence to
THE TOOTHED WHALES (DENTICETE).
Except the possession of teeth, no other available common character need here be given.
THE SEAL-TOOTHED WHALES (PHOCODONTIA OR ZEUGLODONTIA).
RESTORATION OF SKULL (A), AND TOOTH (B) Of ZEUGLODON. (After Gaudry.)
We begin with these, as they are supposed by some authorities to be intermediate between the Seals and Whales. This extinct family, judging from the various mutilated remains found, comprised several different genera. The most notable of these are Zeuglodon, Squalodon, and Phocodon. The ZEUGLODONS may have attained a length of fifty or sixty feet. Their vertebral column was cetacean in character, but the neck-bones were separate, though considerably flattened from before backwards. Some assert that their skull bore resemblances to that of the Seals in several respects. Their brain-cavity undoubtedly was remarkably small, and relatively less than that of known Whales; but the supposed Seal-like skull structure is open to question. The teeth were of two kinds: those in front being conical, pointed, and lengthened; and those behind laterally compressed, serrate, and double-rooted. The dental formula is stated to have been—Incisors, 3–3 3–3; canines, 1–1 1–1; molars, 5–5 5–5 = 36. Hind limbs may have been absent, but the fore limbs suggest rather than furnish precise data showing approximation to the Seals. The SQUALODONS are known chiefly from the skull, which, as a whole, has strong resemblances to those of the curious Amazon Dolphins, called Inia and Pontoporia, but the dentition, however, agrees rather with that of the Dolphin of the Ganges, Platanista. They possessed a long, narrow snout, but no special crest on the summit of the head, and the blow-holes were situate as in the foregoing three last-mentioned living genera. Van Beneden has given the following formula of the dentition:—Incisors, 3–3 3–3; canines, 1–1 1–1; molars, 11–11 11–11 = 60. Their teeth in most respects resembled those of the Zeuglodons. Much less is known of the PHOCODONS, our information regarding them being chiefly derived from the teeth. These latter were not unlike the rearmost of those of the Zeuglodons and Squalodons. The Zeuglodons have been found in the Eocene and Miocene strata of North America. The first remains from Alabama were considered by Dr. Harlan to be those of an enormous reptile (Basilosaurus), but Professor Owen proved their Mammalian character from the teeth being implanted in distinct sockets. The Squalodons and the Phocodons have not only been found in the United States, but in Australia, and in France, Belgium, Austria, Italy, and England. Of course nothing is known respecting their habits other than what may be legitimately inferred from their skeletal peculiarities. To all intents and purposes, so far as we know, the balance lies in favour of their having had the habits of Whales. They may have been river-frequenters, and judging from the dentition their food would be similar to that of the Ganges and Amazon Dolphins.