17 



lUADYlTS. 



Ill: A IN. 



. H 



anatomy in which the Sloth differs from ordinary mammal* The 

 number and form of the bone* which compote the trunk, the nature 

 of ita teeth, and the conformation of its stomach and intestines, are 

 all peculiar. The stomach is divided by transverse ligature* into four 

 panto compartment*, which bear a distent resemblance to the four 

 tomaohs of ruminating animali : they do not however exercise the 

 function* of thece organs, nor do the Sloths regurgitate their food, or 

 subject it to a aeoond process of mastication like the ox and the 

 heep. The intestines also are unusually short for an animal which 

 live* entirely upon vegetable substances, scarcely equalling twice the 

 length of the body, whilst those of ruminants frequently exceed ten 

 time* those dimensions. Their simplicity and diminutive size in the 

 Sloths appear to be compensated by the superior and unusual com- 

 plication of the stomach, which, retaining the food for a longer 

 period than in ordinary non-ruminating animals, allows it to be more 

 perfectly macerated, and prepared for the action of the absorbent 

 vesaola which imbibe its nutritious particles in its passage through 

 the intestines. The number of vertebra in the necks of mammals is 

 generally seven, so that the whales and dolphins, which have scarcely 

 any neck at all, as well as the giraffe and camel, which have it 

 developed in a most unusual degree, are all found to agree in this 

 particular, however widely they differ in other respects : the B. 

 triitiictyliu alone forms an exception to this otherwise universal rule, 

 in having nine cervical vertebrae. What renders this circumstance 

 still more surprising is, that the neck of the Sloth (/(. tridactyltu), 

 notwithstanding its two supernumerary vertebrae, is far from long 

 being on the contrary much too short for its long fore legs if it were 

 compelled to seek its food on the ground like other animals. But 

 this defect is compensated, as well by the nature of the situation 

 which it habitually occupies, suspended from the horizontal branches 

 of the trees, as by its power of using the fore paw as a hand in 

 conveying the food to its mouth, which, notwithstanding the rigidity 

 of its members, it does with great address with one paw, whilst it 

 clings firmly to the branches by means of the other three. 



The dental system of the Sloths is the most simple that can well be 

 conceived. They have no incisor teeth, but canines and molars only ; 

 and in the IS. tridactyltu the canines are diminutive, and in all respects 

 very similar to the other teeth. The molar teeth are universally eight 

 in the upper jaw and six in the lower, four and three on either side 

 respectively. Their construction is most simple, consisting merely of 

 a cylinder of bone, enveloped in enamel, and hollow at both ends, at 

 the upper by continual detrition, and at the under by default of ossifi- 

 cation. They have no lamina of enamel penetrating the body of the 

 tooth, as in other herbivorous animals, which renders them such 

 effective instruments in grinding and masticating vegetable substances. 

 Hence it results, that the mastication of the Sloth must be extremely 

 imperfect, though the defect of dentition is probably compensated in 

 some degree by the superior complication of the stomach. 



The genera Bradypat and Cholceput, together with the extinct fossil 

 animals which have been called Megatherium and Megalonyx, and 

 which, with the form and organisation of a sloth, nearly equalled the 

 elephant in size, constitute the Cuvierian family Tardigrada. Besides 

 the difference of the canine teeth, which are completely developed in 

 Ckolttptu and in Bradypiu, of the same form and subject to the same 

 detrition as the molars, these two genera are distinguished from one 

 another by the number of toes on the fore feet, which are three in the 

 Bradypiu and only two in the Ciiolirpiu ; by the comparative length 

 of (he fore-arms, which are much longer in the former than in the 

 latter ; by the number of cervical vertebra; in the Bradyput, as already 

 mentioned ; by the equally unusual number of ribs in Chobtptu, which 

 amount to no fewer than forty-six, the greatest number hitherto 

 found in any mammal, the species of Bradypiu having but thirty-two ; 

 and by numerous other modifications which it is unnecessary to 

 enumerate. 



The Sloths are known to bring forth and suckle their young like 

 ordinary quadrupeds. For this purpose they have two mammip, 

 which are situated on the breast ; and the young Sloth, from the 

 moment of its birth, adheres to the body of its parent till it acquires 

 sufficient size and strength to shift for itself. The head of the Sloth 

 or Ai (B. tridactyltu) is short, the face small and round like that of 

 the American monkeys, the ears concealed in the long hair which sur- 

 rounds them, the eyes small and deeply sunk in the head, and the tail 

 a mere rudiment This species is found only in the most gloomy and 

 retired tropical forests of South America. The Indians like its flesh, 

 and are in continual pursuit of it. 



In the list of specimens of Mammalia in the British Museum three 

 specie* of Bradypat and one of Ckolaptu are given. Several varieties 

 have been described. 



B. tridactyltu, the Sloth or AL It has a short round head, furnished 

 with coarse shaggy hair, disposed on the crown in verging rays, like that 

 of the human species ; the face is of a yellowish colour, covered with 

 very short hair, whilst that of the body and extremities is universally 

 long and shaggy ; the eyes are encircled by a brown ring ; the hair of the 

 body varied with irregular patches of dark and light brown, or silvery 

 white ; between the shoulders there is an oval patch of short orange- 

 ooloured hair, of a finer quality than that found on other parts of the 

 body, and divided in the centre by a longitudinal black stripe ; the 

 throat and breast are frequently of a light straw-colour. The texture 



of the hair is altogether peculiar, and more nearly resembles dry hay, 

 or gran shrivelled and withered by the sun, than the hair of ordinary 

 quadrupeds. It U coarse and flattened at the extremity, but as small 

 at the root as the finest spider's web ; and it* dry and withered appear- 

 ance forms the Ai's principal security against its pursuers, as it renders 

 it extremely difficult to detect it whilst at rest among the branches 

 covered with bark and moss of the same colour. It U only when in 

 motion that it can be readily distinguished from the trunk beneath 

 which it hangs suspended. In other respects different individuals of 

 this species differ considerably from one another in the shades and 

 disposition of their colours, and in the intensity of the mark between 

 the shoulders ; some even want this latter mark altogether, others are 

 of a uniform ash-colour over the whole body, and there are others 

 still which have the hair of the head parted in the centre, and hanging 

 down on each side; but whether these constitute distinct specie*, 

 or mere varieties of the common Ai, is a point hitherto undetermined : 

 the cabinets of Europe do not afford sufficient materials for an exten- 

 sive comparison, and no naturalist has ever examined the Ais with 

 this view in their native regions. 



/(. torquatut, the Oipakeiou, is a very distinct species, even in the 

 bony structure of its cranium. Its face is naked, and of a black 

 colour ; the hair of ita body less flattened and withered-looking than 

 in the common species ; the forehead, temples, chin, throat, and breast 

 covered with reddish or rust-coloured hair, slightly frizzled ; on the 

 crown of the head it is long and yellow, and on the rest of the body 

 pale orange ; but the most distinguishing mark of the species is a 

 large block collar which completely surrounds the neck. Beneath thin 

 outer coat there is an inner one of very fine fur, which is of a dorlr 

 brown colour on the collar, but gradually diminishes in intcn>it_y 

 towards the croup, where it is entirely white. 



Both these species feed upon the leaves of trees, and bring forth 

 but a 'single young one at a birth. When in motion in the forests 

 they emit a feeble plaintive cry, resembling the word ' Ai,' and which 

 is the origin of the name they bear among the Europeans settled in 

 America. They are extremely retentive of life, and have been seen to 

 move their legs and exhibit other symptoms of vitality a full half- 

 hour after being deprived of the heart and other viscera. 



B. gularii, the Yellow-Faced Sloth, is supposed by some to be a 

 variety of B. tridactyliu. 



BRAGANTIA, a genus of plants belonging to the natural order 

 Arittolochiacea;. One of the species, B. tomentota, is said by Dr. 

 Horsfield to be intensely bitter, and to be used as a medicine 

 in Java, 



BKAIN, a soft and pulpy organ, which in man occupies the C-M ity 

 of the cranium, and forms one of the central masses of the nervous 

 system. [NERVOUS SYSTEM.] In man and all the higher animals the 

 nervous system consists of four distinct parts the white threads 

 called Nerves, knots or masses of nervous matter situated along the 

 course of the nerves called Ganglions, a long cord of nervous matter 

 filling the cavity of the vertebral or spinal column called the Spinal 

 Cord, and a large mass of nervous matter now generally considered 

 as a continuation and expansion of the spinal cord called the Brain. 

 The Spinal Cord and Brain constitute the two central masses of the 

 nervous system, that is, the immediate seat of the functions peculiar 

 to this system. 



The general moss of nervous matter designated under the common 

 term Brain, together with its membranes, vessels, ami nerves, com- 

 pletely fills the cavity of the skull. This mass i< <lhi.lrd into three 

 parts, the Cerebrum, or brain proper, which occupies the whole of the 

 superior part of the cavity of the cranium ; the Cerebellum, much 

 smaller than the cerebrum, whence its name, Little Brain, which 

 occupies the lower and bock part of the cavity of the cranium ; and 

 the Medulla Oblongata, by much the smallest portion of the mass, 

 situated at the basis of the cavity beneath the cerebrum and cere- 

 bellum. The medulla oblongata passes out of the cavity of the 

 cranium into that of the vertebral canal by the foramen magnum of 

 the occipital bone, being continuous with and forming the commence- 

 ment of the spinal cord. 



This general nervous mass is closely enveloped in three distinct 

 membranous coverings, two of which have been called ' inatros," 

 from the fanciful notion that they give rise to all the other membranes 

 of the body. The external covering termed Dura Mater, from its 

 being of a firmer texture than the other two membranes, inclose* 

 the brain with all its appendages, and lines the whole internal surface 

 of the bones of the cranium. It is of a fibrous texture, the com- 

 ponent fibres interlacing each other in every possible direction, ami 

 forming by their firmness and density the thickest and strongest 

 membrane of the whole body. By its external surface the dura 

 mater adheres everywhere to the inner surface of the cranium, just 

 as the periosteum adheres to other bones. \Vh. n torn from the 

 cranium this surface appears somewhat rough and irregularly spotted 

 with bloody points, which are the lacerated orifices of vessels that pass 

 between the membrane and the surrounding bones. These vessels 

 are much more numerous in the young than in the adult, and are 

 most abundant at the sutures or junctions of the bones that compose 

 the skull. The inner surface of the dura mater, which is shining 

 and smooth, is lubricated and kept in a state of moisture by a fluid 

 secreted by its own vessels. This membrane performs a twofold 



