The lower jaw is very straight: it projects a little, in front and behind, where it is jointed with the upper jaw, there is no upright portion or branch, or ascending ramus. The last back tooth is just in front of a curved piece of bone called the coronoid process, the base of which is on a level with the line of the teeth.
This Sloth has seven neck bones (cervical vertebræ), and the last one has a very small and rudimentary rib attached to it on either side. There are no less than twenty-three dorsal vertebræ found to be with ribs. The Unau has a clavicle which is much smaller in the other group. It has no tail. The structure of the ankle joint enables it to turn in, even more than that of the Three-clawed Sloth. As the habits of the Unau Sloth are the same as those with three claws, and all live in the same great district, these anatomical distinctions are very interesting, and relate to their remote ancestors, being hereditary legacies, which are of little or no importance in assisting the creature merely to live. One of the differences between the Sloths is singular. The Unaus have a very remarkably formed stomach, which may be said to be double. The first stomach is large and rounded, but it is contracted behind, and then formed into a kind of conical appendix. This appendix is doubled from left to right, and its cavity has a fold at its opening into the stomach. It forms a special part of the first stomach. Then it is to be noticed, that where the food enters the stomach, or at the opening, which is called the cardia, there is a pouch, looking like a bag at the end of the tube which runs down from the gullet to the stomach. This is the second part of the first stomach: and the third is a tube-like space which connects the cardia with the stomach far away to the left. These three cavities form the first stomach. The second stomach is of a slender form, and is very much smaller than the other. Its walls are thin for the first half of its length, but towards the spot where the gut commences (the pylorus) they are thick and muscular. A small fold occurs midway. There is a fold in the body of the smaller or second stomach, and there is a little hollow there with glands in it, and it is called the appendix to the second stomach.
STOMACH OF SLOTH.
The stomach is thus rather complicated, and its internal mucous membrane is so thrown into folds, and made into hollow spaces, that it occupies much more space than if it were a simple bag. This plan is also well seen in those ruminating animals which, like the Ox, live entirely upon vegetable substances; and it is evident that the diet of the Sloth bears some relation to the complicated stomach.
In the Ai, the appendix to the second stomach is larger than that of the Unau Sloth, and is more complicated.
HOFFMANN’S SLOTH.[61]
This is a Sloth with two clawed fingers on the fore, and with three claws on the hinder extremities. Living specimens are occasionally brought to Europe, especially from Porto Rico, so that its general appearance may now and then be studied at the Zoological Gardens, in the Regent’s Park. If it be looked at there in the day-time, it certainly merits the name of Sloth, for it resembles a bundle of long, light, brown hair, fixed on the top of a bar of wood close to an upright branch, or huddled up in a corner on the ground; but in the morning, and also late in the evening, the creature begins to move slowly, and to look out for the food put for its use on the floor of the den. All the Hoffmann’s Sloths have pale brown hair, whiter at the tips, and a white face, showing a brown band across the nose, extending to a ring round each eye. They have also a long and full crest of hair on the neck, and the hair on the limbs is darker than that of the rest of the animal. Dr. Peters, who discovered this Sloth, examined the skeleton, and found only six vertebræ in the neck, and in this it differs from the Cholœpus just noticed.
When its food, consisting of carrots and lettuce, and bread-and-milk, is put down in the morning it is soon in movement, and enjoys its meal hanging down from a bar with its hind legs, and resting its back on the floor of the cage. It seizes the food between the claws and the long straight palm of the fore-foot, and passes it into its mouth, chewing actively with the molar teeth, especially with the first, which are sharp. It cares little for the spectators, and when it has finished, slowly mounts up into a corner of its little den and settles down to sleep. In the evening it becomes lively, for it is, and, indeed, all Sloths are, nocturnal in habit. The hairless snout, of a light red tint, the absence of “smellers,” the little eyes with a few hairs around them, and the broad forehead, give the animal a curious appearance. The hair is brushed back on the forehead, and comes around the very small ears on to the cheeks, and is whitey-brown, and this same tint is seen over the whole of the back in long slender hairs. But the under hair is light red or red-brown. The long and slender hand, with its two claws, contrasts with the rather bulky upper part of the limbs, and the flesh-coloured palms are very remarkable.
