Page:Encyclopædia Britannica, Ninth Edition, v. 15.djvu/481

MANATEE 457 fuuctionless, and altogether disappear before the animal is full-grown. There is besides, on each side of the hinder part of both upper and lower jaws, a parallel row of molar teeth, similar in characters from the beginning to the end of the series, with square enamelled crowns raised into tuberculated transverse ridges, something like those of the Tapir and Kangaroo. The upper teeth have two ridges and three roots ; the lower teeth have an additional posterior small ridge or talon, and but two roots. These teeth succeed each other from before backwards, as in the Proboscidea, those at the front of the mouth being worn out and shed before those at the back are fully developed. There are altogether about eleven on each side of each jaw, but rarely more than six are present at one time. The brain is remarkably simple in structure, its hemispheres exhibiting none of the richness of convolution so character istic of the Cetacea. The stomach is compound, being divided by a valvular constriction into two principal cavities, the first of which is provided with a singular glandular pouch near the cardiac end, and the second with a pair of elongated, conical ccecal sacs or diverticula, the use of which is by no means obvious. The cascum is bifid. The kidneys are simple. The heart is broad and flat, with the apex deeply cleft between the ventricles. The prin cipal blood-vessels form very extensive and complex retia miralUia. The lungs are remarkably long and narrow 7 , as owing to the very oblique position of the diaphragm the thoracic cavity extends very far back over the abdomen. The mammary glands of the female are two in number, situated just behind and to the inner side of the origin of the pectoral limb. The red corpuscles of the blood are among the largest of those of any members of the class, averaging in diameter, according to Gulliver, -g- T ^<j- of an inch. Manatees pass the whole of their life in the water, inhabiting bays, lagoons, estuaries, and large rivers, but the open sea, so congenial to the Cetacea, is quite unsuited to their peculiar mode of life. As a general rule they prefer shallow water, in which, when not feeding, they lie near the bottom, supporting themselves on the extremity of the tail, or slowly moving about by the assistance of the fore limbs, the tips of which are just allowed to touch the ground, and only raising the top of the head above the surface for the purpose of breathing at intervals of two or three minutes. In deeper water they often float, with the body much arched, the rounded back close to the surface, and the head, limbs, and tail hanging downwards. The air in the lungs obviously assists them to maintain this position, acting in the same manner as that in the air-sac of fishes. Their food consists exclusively of aquatic plants, on which they browse beneath the water much as terrestrial Ungulates do on the green pastures on shore. They are extremely slow and inactive in their movements, and perfectly harmless and inoffensive, but are subject to a constant persecution from the inhabitants of the countries in which they dwell for the sake of their oil, skin, and flesh. Frequent attempts have of late been made to keep specimens alive in captivity, and sometimes with con siderable success, one having lived in the Brighton Aquarium for upwards of sixteen months. It was fed chiefly on lettuce and endives, but would also eat leaves of the dandelion, sow-thistle, cabbage, turnip, and carrot. From this and other captive specimens some interesting observations upon the mode of life of the animal have been made. One of these is the free use it makes of its fore- limbs. From the shoulder-joint they can be moved in all directions, and the elbow and wrist permit of free extension and flexion. In feeding they push the food towards their mouths by means of one of the hands, or both used simultaneously, and any one who has seen these members thus employed can readily believe the stories of their carrying their young about under their arms. Still more interesting and quite unique among Mammals is the action of the peculiar lateral pads formed by the divided upper lip, thus described by Professor Garrod : " These pads have the power of transversely approaching towards and receding from one another simultaneously (see fig. 1, A and B). When the animal is on the point of seizing (say) a leaf of lettuce, the pads are diverged transversely in such a way as to make a median gap of considerable breadth. Directly the leaf is within grasp the lip-pads are approximated, the leaf is firmly seized between their con tiguous bristly surfaces, and then drawn inwards by a backward movement of the lower margin of the lip as a whole." The animal is thus enabled by the unaided means of the upper lip to introduce food placed before it without the assistance of the comparatively insignificant lower lip, the action greatly recalling to the observer that of the mouth of the silkworm and other caterpillars in which the mandibles diverge and converge laterally during mastication. When out of water the Manatee is an ex tremely helpless animal ; and, although statements are frequently met with in books of its voluntarily leaving the water for the purpose of basking or feeding on shore, all trustworthy observations of those acquainted with it, either in a state of nature* or in captivity, indicate that it has not the power of doing so. None of the specimens in con finement have been observed to emit any sound. Manatees, though much less numerous than formarly, are still occasionally found in creeks, lagoons, and estuaries in some of the West India Islands, and at various spots on the Atlantic coast of America from Florida as far south as about 20 S. lat., and in the great rivers of Brazil, almost as high as their sources. They are also met with in similar situations on the opposite African coast, from about 16 N. to 10 S. lat., and as far into the interior as Lake Tchad. Its range may even extend, if native reports obtained by Schweinfurth are correctly interpreted, to the river Keebaly, 27 E. long. The American Manatee (M. australis, Tilesius) was thought by Dr Harlan to be divisible into two species, one inhabiting Brazil arid the other the West Indies and Florida. To the northern form he gave the name of M. latirostris, but the distinction is not now generally recognized. On better grounds the African Manatee was separated by Desmarest, under the name of J/. senegalensis, and there are certainly constant although not very important cranial characters by which it can be dis tinguished from its American congener, among which the following may be cited : the anterior part of the rostrum is shorter, shallower, and altogether smaller ; the orbit is smaller ; the zygomatic process is more deep and massive ; the malar bone is deeper from above downwards; the upper margin of the anterior nares is narrower and with a smooth and rounded instead of a tliin and serrated edge; the upper surface of the frontal is flat, instead of concave; the foramen magnum and occipital condyles are narrower from side to side, and the symphysis of the mandible smaller and shallower. For an account of the animals most nearly allied to the Manatee, the Rhythm, or "Northern Manatee" as it is sometimes called, and the Dugong, as well as the various extinct kindred forms, see MAMMALIA, pp. 390, 391. Bibliography. "W. Yrolik, Bijdraycn tot dc Dicrkunde, 1851 ; J. Murie, " On the Form and Structure of the Manatee," Trans. ZooL Soc. Lond., vol. viii. p. 127, 1872, and "Further Observations on the Manatee," Ibid., vol. xi. p. 19, 1880; A. H. Garrod> "Notes on the Manatee recently living in the Zoological Society s Gardens," Ibid., vol. x. p. 137, 1875; H. C. Chapman, "Obser vations on the Structure of the Manatee," Proc. Acad. Nat. Sciences of Philadelphia, 1875, p. 452 ; A. Crane, "Notes on the Habits of the Manatees in Captivity in the Brighton Aquarium," Proc. Zool. Soc. Land., 1881, p. 456. ( w - H - F -)

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