Page:Encyclopædia Britannica, Ninth Edition, v. 15.djvu/407

Rh EDENTATA.] MAMMALIA 385 both North and South America, were intermediate between those of the existing Bradypodidee and the Myrmccophagidiv, combining the head and dentition of the former with the structure of the vertebral column, limbs, and tail of the latter. Almost all the known species are of comparatively gigantic size, the smallest, Coslodon cscrivan- ensis, exceeding the largest existing Anteater, and the Megatherium being larger than a Rhinoceros. The dentition is usually on each FIG. 35. Section of Uppar Molar Teeth of Megatherium, x J. From Owen. side, as in the Sloths, but in Ccelodon f. This genus, and in a still more marked degree Megatherium, differ from all the others in the details of the structure of the teeth. They are very deeply implanted, of prismatic form (quadrate in transverse section); and the component tissues hard dentine (fig. 35, d), softer vaso-dentine (v), and cementum (e) are so arranged that, as the tooth wears, the surface always presents a pair of transverse ridges, thus producing a triturating apparatus comparable to the &quot; bilopho- dont &quot; molar of Dinotherium, Tapirua, Manatus, Macropus, and others, though produced in a different manner. In all the other genera the teeth are more or less cylindrical, though sometimes later ally compressed or even longitudinally grooved on the sides, and on the grind ing surface the prominent ridge of hard dentine follows the external contour, and is surrounded only by a thin layer of cementum, as in the existing Sloths. The genera of which the remains are best known are Mylodon (fig. 37), Lesto- don, Scelidothcrittm, Gfryphotherium, and Mcgalomjx. In the last-named the anterior tooth of both upper and lower jaws is large and removed by a consider able interval from the others. The osteological characters of these genera have been fully described in the works of Cuvier, Owen, Burmeister, Leidy, Gervais, Keinhardt, and others. No Eocene Edentates have yet been found in America. In the Miocene of the Pacific coast of North America some remains have been discovered, assigned FIG 36. Lower Jaw and Teeth ,,,-,, T. T &quot;,i ot Megatherium. From Owen, by Marsh to the genus Moropus, the type of a distinct family, the Moropidw. There are two species, one about as large as a Tapir, and one nearly twice that size. In the Lower Pliocene, well-preserved remains of Edentates of very large size have been found at several widely separated localities in Idaho and California. These belong to the genus Morotherium, of which two species arc known. East of the Rocky Mountains, in the Lower Pliocene of Nebraska, a large species apparently of the genus Moropus has been discovered. None of these have as yet been fully described or figured. Marsh believes that North America was the ori ginal home of the Edentates, and that they spread to the southern portion of the continent towards the close of the Tertiary period. Family MYRMECOPHAGIDJE. Externally clothed with nair. No teeth. Head elongated. Mouth tubular, with a small terminal aperture, through which the long, vermiform tongue, covered with the viscid secretion of the enormous submaxillary glands, is rapidly protruded in feed ing, and withdrawn again with the adhering particles of aliment, which are then sucked into the pharynx. In the maiius, the third toe is greatly developed, and has a long falcate claw ; the others are reduced or suppressed. The pes has four or five subequal digits with claws. Posterior dorsal and lumbar vertebrae with ad ditional interlocking zygapophyses. Tail long, sometimes prehen sile. Placenta dome-like or discoidal. The animals of this family are the &quot; Anteaters&quot;^ar excellence. They feed exclusively on animal substances, mostly insects. One species is terrestrial, the others arboreal; none burrow in the ground. They are all inhabitants of the Neotropical region. Myrmecopliaga. Skull greatly elongated and narrow, its upper surface smooth and cylindriform. Anteriorly the face is produced into a long, tubular rostrum, rounded above and flattened below, and with terminal naves, and composed of the mesethmoid ossified for more than half its length, the vomer, the maxillse, and the long and narrow nasal bones, the premaxilloa being extremely short and con fined to the margin of the anterior naves. The zygomatic arch is in complete, the styliform malar only articulating with the maxilla in front, and not reaching to the very short zygomatic process of the squamosal. The lacrymal foramen is in front of the margin of the orbit. There are no post-orbital processes to the frontals or any other demarcation between the orbits and the temporal fossa?.. Palate ex- FKJ. 37. Skeleton of Mylodon robmtus (Pleistocene, South America). From Owen. tremely elongated, and produced backwards as far as the level of the external auditory meatus by the meeting in the middle line of the largely developed pterygoids. The glenoid fossa a shallow oval facet, with its long diameter from before backwards. Mandible very long and slender, with an exceedingly short symphysis, no distinct coronoid process, and a slightly elevated, elongated, flattened, con- dylar articular surface. Vertebras : C 7, D 15-16, L 3-2, S 6, C 31. Clavicles rudimentary. In the manus, the first digit is very slender, the second also slender, with compressed phalanges of nearly equal length. The third digit is immensely developed ; though its proximal phalanx is extremely short, its ungual phalanx is so long that the entire length of the digit exceeds that of the second. The fourth has a long and rather slender metacarpal, and three phalanges diminishing in size, the ungual phalanx being very small. The fifth has the metacarpal nearly as long, but not so stout as the fourth, and followed by two small phalanges, the last rudimentary and conical. Claws are developed upon all but the fifth. In walking the toes are kept strongly flexed, and have their points turned upwards and inwards, the weight being supported upon a callous pad ovev the end of the fifth digit, and by the dorsal sur faces of the third and fourth digits. The hind feet are short and rather broad, with five subequal claws, the fourth rather longest,_the first shortest; the whole sole is placed on the ground in walking. Body rather compressed, clothed with long, coarse hair. Tail about as long as the body, and covered with very long hair ; not prehensile. Ears small, oval, erect. Eyes very small. Stomach consisting of a subglobular, thin-walled, cardiac portion, and a muscular pyloric gizzard with dense epithelial lining. No ilec- colic valve, and a short wide ill-defined crocum. Mamma? two, pectoral. There is one species, M. jiibata, the Great Anteater, or Ant Bear, measuring 4 feet in length without the tail, and upwards of 2 feet in height at the shoulder. Its prevailing colour is grey, with a broad black band, bordered with white, commencing on the chest, and passing obliquely over the shoulder, diminishing gradu- ally in breadth as it approaches, the loins, where it ends in a point. XV. 49