Natural History: Mammalia/Bradypodidæ

by Philip Henry Gosse

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Family I. Bradypodidæ.

(Sloths.)

Until recently, naturalists laboured under much ignorance of the natural habits of these strangely formed animals: and hence rash and unfounded statements were made, reflecting even on the wisdom of the Creator. The name by which they are still distinguished is calculated to perpetuate these erroneous opinions, and hence we should feel unwilling to use it, were there any other title by which we might intelligibly designate the genus.

The sphere of action of these animals is amongst the branches and foliage of the dense forests that border the mighty rivers of South America. Their mode of progression is quite peculiar; as they cling to the horizontal or inclined branches with the back downward, and move onward in a style which may be compared to a feat that sailor-boys are fond of performing, going up the mainstay "hand over hand;" only that the Sloth uses all his limbs in the operation. Their food consists of the leaves of trees, with their buds and young shoots. To this singular mode of life the structure of the Sloths is adapted, with the same consummate wisdom and skill, that is manifest in all the other works of God.

The dentition of these animals is thus expressed—Inc. $_{0}^{0}$; can. 1—1/1—1; mol. 4—4/3—3;$=$18. The molars are very simple, each consisting merely of a cylinder of bone, enveloped in enamel: their surfaces are hence always concave, the soft interior wearing faster than the enamel edge; and there are no folds or laminæ of this latter substance penetrating the body of the tooth, as in most other animals. The canines are of similar formation, but are pointed. The fore limbs are generally lengthened; to such a degree that in attempting to move on a plane surface the animal is compelled to rest on its elbows. The pelvis is very large, and hence the thigh bones are set so wide apart that the knees cannot be made to approach each other. The palms or soles of the feet are set on obliquely, facing inward, as we saw in the Apes, and for the same purpose. The bones of the feet are exceedingly rigid, being, to a considerable extent, soldered, as it were, together; and the toes are terminated by powerful hooked claws of enormous length, which in a condition of rest are drawn down upon the palm and wrist, and can be extended only by the will and muscular effort of the animal. It is easy to see how these characters are suited to a hanging and climbing habit: the sharp bent claws forming effective hooks for holding on, the immovable limbs for maintaining a firm hold, the oblique articulation of the feet and thighs for embracing a branch, and the great length of the arms for seizing a fresh hold, or for drawing the twigs and leaves to the mouth. In other respects, also, the same Divine care is manifest. Though the structure of the molar teeth will not admit of the food being much ground in the mouth, and the intestinal canal is unusually short for vegetable feeders,—yet this is compensated by the volume and complexity of the stomach, which is divided into four compartments, scarcely less elaborate than those of the Ruminantia. The body is clothed with long, coarse hair, somewhat resembling dried grass, or the tree-moss (Tillandsia) which hangs in immense bunches from the tropical forests. The face is short and round, like that of a Monkey. There are but three toes on the hind-feet, and either two or three, (according to the genus,) on the fore ones: the toes are enveloped in the skin.

The two genera which comprise this Family, containing not more than three or four known species, are limited to the tropical regions of South America.

Genus Bradypus. (Linn.)

The characters already enumerated as belonging to the Family are more strongly marked in this genus than in the Unau (Cholœpus). It is also distinguished by having three claws on the forefoot or hand: the thumb and little toe barely visible as rudimentary bones in the skeleton, being quite concealed by the skin. It possesses a tail, which, however, is short. The neck is lengthened, and endowed with a more complete power of rotation by the addition to it (in effect) of two bones; which, however, by their possession of rudimentary ribs, are proved to belong to the back; leaving the number of true neck-bones seven, as in all other Mammalia.

The Common Aï (Bradypus tridactylus, Linn.) has a short round head, clothed with long rough hair, which diverges from the crown, like the human hair. The body is covered with long hair, coarse and flattened at the extremity, but as fine at the root as a spider's thread. Its colours are light and dark brown, dispersed in irregular patches, and varying much in individuals; an oval patch of finer shorter hair, of an orange-colour, is situated between the shoulders; the face, throat, and breast are of a pale straw-yellow. It is about as large as a Cat. The expression of its countenance is very melancholy, as is the sound of its voice, which resembles the syllables aï, feebly uttered in a plaintive tone.

We have already described the ordinary habits of the Aï in a state of freedom, as witnessed by Mr. Waterton, and other travellers. Specimens

THE AÏ.

THE AÏ.

have also been repeatedly brought to Europe, and observed in captivity. Mr. Burchell remarked of some in his possession that they assumed during sleep a position of perfect ease and safety on the fork of a tree, their arms embracing the trunk, their backs resting on the angle of a branch, and their heads reclining on their own bosoms. The animal is thus rolled up nearly in the form of a ball; the entire vertebral column, including the neck, assumes a nearly circular curve, and not only is the weight of the whole body maintained in an attitude of ease and safety, but the head is supported between the arms and chest, and the face lies buried in the long wool which covers those parts, and is thus protected during sleep from the myriads of insects which would otherwise attack it.^[1]

1. Prof. Buckland, in Linn. Trans. 1835.