143 MAMMALIA. 



The Bottle-heads (Hyperoodon, Lacep.) — 



Have the body and muzzle nearly similar externally to those of the Dolphins properly so called, but 



the cranium is laterally elevated by vertical bony partitions : most usually there are found only two 



small teeth in the fore-part of the lower jaw, which do not always appear externally ; the palate is 



studded with small tubercles, [and there is a small dorsal fin]. 



Hut one species is known, which attains a length of five-and-twenty feet, and perhaps more, [Delph. edentulus, 

 Schreb. ; D. buUkopf, Lacepede; D. bidentatus, Hunter; 1). Hunteri, Desm. ; the Bottle-nosed Whale of Hunter]. 

 — It is taken in the British Channel and the North Sea, and is often designated Baleine a bee. 



[The Diodons {Diodon, Lesson)— 



Principally differ from the preceding in having a flattened forehead : their lower jaw is much larger 



than the upper, and convex. 



There is a species in the Mediterranean (Delph. Desmaresiii, Risso), fifteen feet in length ; a specimen of which, 

 or of another closely allied, was cast on shore on the coast of Scotland (D. Koieerbii, Desm. and Blainv.) Several 

 others are said to belong to this subdivision.] 



The Narwhal (Monndon, Lin.) — 

 Has no teeth, properly so called ; but very long and slender-pointed tusks implanted in the inter- 

 maxillary bones, and directed in the line of the axis of the body. The form of their body and head 

 greatly resembles that of the Porpoises, [and still more the Beluga, as noticed by Prof. Bell; the 

 swimming paws being also remarkably small, and the dorsal fin wanting, as in the latter animal]. 



( inly one species is known (.Won. monocero.t, Lin. ; {Narwhalut microcephalia, Bonat., Lacep., Desm.] ), the tusk 

 of which, grooved spirally, and sometimes ten feet long-, was formerly termed the horn of the Unicorn. This 

 animal possesses the germs of two tusks, but it is seldom that both become equally developed. That on the left 

 side usually attains its full growth, while the other remains permanently concealed within its socket, its develope- 

 ment having been prevented by its interior cavity becoming too rapidly tilled with the deposition of ivory, which 

 thus obliterates its gelatinous core. According to the description of the Narwhal, it is scarcely more than twice 

 or three times the length of its tusk ; the skin is marbled with brown find whitish ; it has a convex muzzle, small 

 mouth, spiracle placed on the top of the bead, and no dorsal tin, but merely a projecting crest the whole length of 

 its spine. The teeth are sometimes found perfectly smooth. 



[We may here mention, at the conclusion of the Cctacea with moderate-sized heads, an extremely 



remarkable genus, — 



Thk I ma, d'Orbigny,— 



Which has the external form of the Dolphins, properly so called, with some coarse bristly hairs on the 

 snout: the spiracle is placed far backward, above the swimming-paws; the lips are deeply cleft to 

 beneath the eye ; and there is a small dorsal fin, and proportionally large auditory aperture. 



The only species known (I. Boliviensis, d'Orb'.) is remarkable for occurring thousands of miles from the sea, 

 appearing to inhabit only the remote tributaries of the Amazons, and the elevated lakes of Peru : the singular 

 character of possessing bristly hairs on the snout has also been observed in them when very young. This species 

 has large swimming-paws, and thirty-four teeth on each side above and below, all of them rough, marked with 

 deep and interrupted furrows, and of an irregular mammalory shape behind, which is very peculiar. A female 

 specimen measured seven feet long, and the males are stated to be double that size : colour variable, commonly 

 pale blue above, passing into a roseate hue beneath. It comes more frequently to the surface than the marine 

 species, and is generally met with in troops of three or four individuals.] 



The remaining Cetacea have the head so very large, as to constitute one-third or even half 

 the entire length ; but neither the cranium nor the brain participates in this disproportion, 

 which is wholly due to an enormous developement of the bones of the face. 



The Cachalots {Physefer, Lin.), — 



Are Cetacea with a most voluminous head, excessively enlarged, particularly in front ; in the upper jaw 

 of which there are neither teeth nor baleen {whalebone), or, if any of the former, they are small, and 

 not projecting beyond the gum ; but the lower jaw, straight, elongated, and corresponding to a groove 

 in the upper one, is armed on its two sides with a row of cylindrical or conical teeth, which enter into 

 corresponding cavities of the upper jaw when the mouth is closed. The superior portion of their 

 enormous head consists almost entirely of large cavities, separated and covered by cartilages, and filled 

 with an oil that becomes concrete on cooling, well known in commerce by the name spermaceti, a 



