1902 Encyclopedia > Manatee

Manatee




MANATEE, an animal belonging to the order Sirenia, for the general characters and position of which see MAMMALIA (p. 389). The name Manati was apparently first applied to it by the early Spanish colonists of the West Indies, in allusion to the band-like use which it frequently makes of its fore limbs ; by English writers from the time of Dampier (who gives a good account of its habits) downwards it has been generally spelt "Manatee." It was placed by Linnaeus in his heterogeneous genus Trichechus, but Storr's name 31-anal-us is now generally accepted for it by zoologists, The question of the specific distinction of the African and American Manatees will be treated of further on, but it will be chiefly to the latter and better known form that the following description applies.

The size of the Manatee has been much exaggerated, as there is no trustworthy evidence of its attaining a greater length than 8 or perhaps 9 feet. Its general external form may be seen in the figure at p. 390 of the present volume, taken from a living example in the Brighton' Aquarium. The body is somewhat fish-like, but depressed and ending posteriorly in a broad flat shovel-like horizontal tail, with rounded edges. The head is of moderate size, oblong, with a blunt, truncated muzzle, and divided from the body by a very slight constriction or neck. The fore limbs are flattened oval paddles, placed rather low on the sides of the body, and showing externally no signs of division into fingers, but with a tolerably free motion at MANATEE 13 the shoulder, elbow, and wrist joints, and with three diminutive flat nails near their extremities. No traces of hind limbs are discernible either externally as internally ; and there is no dorsal fin. The mouth is very peculiar, the tumid upper lip being cleft in the middle line into two lobes, each of which is separately movable, as will be described in speaking of its manner of feeding. The nostrils are two semilunar valve-like slits, at the apex of the muzzle. The eyes are very minute, placed at the sides of the head, and with a nearly circular aperture with wrinkled margins. The external ear is a minute orifice situated behind the eye, without any trace of pirma, The skin generally is of a dark greyish colour, not smooth or glistening, like that of the Cetacea, but finely wrinkled. At a little distance it appears naked, but a close inspection, at all events in young animals, shows a scanty covering of very delicate hairs, and both upper and under lips are well supplied with short, stiff bristles.





The skeleton is remarkable for the massiveness and extreme density of most of the bones of which it is composed, especially the skull and ribs, The cervical region of the vertebral column is short, and presents the great peculiarity of containing only six bones instead of seven, the number usual in the Mammalia, - the only other case being that of one species of Sloth (CholwInts hoffinanni), Another great peculiarity (which, however, seems to be characteristic of all the Sirenia) is that the flat ends of the bodies of the vertebra; do not ossify separately, so as to form disk-like epiphyses in the young state. None of the vertebra are united together to form a sacrum, the rudimentary pelvic bones having no direct connexion with the vertebral column. The number of rib-bearing vertebra appears to vary in different individuals from fifteen to eighteen, and those of the lumbar and caudal region from twenty-five to twenty-nine. The skull (fig. 2) is exceedingly different from that of any of the Whales or Dolphins (order Cetacea), with which the Manatee was formerly supposed to be allied. The cerebral cavity is rather small as compared with the size of the animal, and of oblong form; its roof is formed of the parietal bones as in ordinary mammals. The squamosal has an extremely large and massive zygomatic process, which joins the largely developed malar bone in front. The orbit is small, but prominent and nearly surrounded by bone. The anterior nares taken together form a lozenge-shaped aperture, which looks upwards and extends backwards considerably behind the orbits. Their sides are formed by the ascending processes of the premaxilke below, and by the supraorbital processes of the frontals above, no traces of nasals being found in most skulls, though these bones are occasionally present in a most rudimentary condition, attached to the edges of the frontals, far away from the middle line, a position quite unique among the manimalia. In front of the narial aperture the face is prolonged into a narrow rostrum, forined by the premaxillx, supported below and at the sides by the maxilla. The under surface of this is very rugous, and in life covered by a horny plate. The rami of the mandible are firmly- united together at the -symplaysis, which is compressed laterally, deflected, and has a rugous upper surface ; to this another horny plate is attached, which with that of the upper jaw functionally supplies the place of teeth in the anterior part of the mouth. In the young state there are rudimentary teeth concealed beneath these horny plates, which never penetrate through them, and must therefore be quite functionless, 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 characteristic 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 c2cal sacs or diverticula, the use of which is by no means obvious. The cfecum is bifid. The kidneys are simple. The heart is broad and flat, with the apex deeply cleft between the ventricles. The principal blood-vessels form very extensive and complex retia miralJilia. The lungs are remarkably long and narrow, 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, ,-4-1,-,T 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 considerable 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 forelimbs. 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 a leaf of lettuce, the pads are diverged transversely iii whole." The animal is thus enabled by the unaided of the mouth of the silkworm and other caterpillars in tremely helpless animal ; and, although statements are frequently met with in books of its voluntarily lewiring 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 confinement have been observed to emit any sound.

Manatees, though much less numerous than formerly, river Keebaly, 27° E. long.

The American Manatee (H. attstralis, Tilesius) was thought by Dr Harlan to be divisible into two species, one important cranial characters by which it can be disside, and the symphysis of the mandible smaller and shallower.

For an account of the animals most nearly allied to the extinct kindred forms, see gAMMALIA, pp. 390, 391.

Bibliography. - W. IhYdragen tot de Dicrkunde, 1851 ; J. Murk, " On the Form and Structure of the Manatee," Trans. Zoo!. Soc. Load., vol. viii. p. 127, 1872, and " Further Observations on the Manatee," Ibid., vol. xi. p. 19, 1880 ; A. 11. Garrott, " Notes on the Manatee recently living in the Zoological Society's Gardens,'' Ibid., vol. x. p. 137, 1875 ; H. C. Chapman, " Observations on the Structure of the Manatee," Proc. Acad. lent. Sciences of Philadelphia, 1875, p. 452 ; A. Crane, "Notes on the Habits of the Manatees in Captivity in the Brighton Aquarium," Proc. Zool. Soc. Lend., 1881, p. 456. (W. 11. F.)







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