FIG. 89.--Great Anteater (_Myrmecophaga jubata_). A, Side view of twelfth and thirteenth thoracic vertebrae. B, Posterior surface of second lumbar vertebra. C, Anterior surface of third lumbar vertebra, x 2/3. _az_, Anterior zygapophysis; _az_^1, _az_^2, _az_^3, additional anterior, articular facets; _cc_, facet for capitulum of rib; _m_, metapophysis; _pz_, posterior zygapophysis; _pz_^1, _pz_^2, _pz_^3, additional posterior articular facets; _t_, transverse process; _tc_, facet for articulation of tubercle of rib. (From Flower's _Osteology_.) The first of these characters is the series of additional zygapophyses on the posterior dorsal and lumbar vertebrae; these are very clear in the Anteaters and Armadillos; less clear, but still obviously represented, in the Sloths. In the second place, they all possess a clavicle, rudimentary, it is true, in the Great Ant-bear, but still present. Thirdly, the testes are abdominal throughout life, a character which they share with such lowly-organised animals as the Monotremata and the Whales. Finally, and this is by no means a matter to be overlooked, not only are all the existing members of this group American in range, but there is no evidence to prove that they have ever existed elsewhere. No European or Old-World {164} representatives have as yet been discovered which can be referred to the Anteater, Armadillo, or Sloth type with certainty.[100] Of these American forms, which will be treated of first, the Armadillos are further apart from either Sloths or Anteaters than the last two are from each other. The name XENARTHRA has been suggested for the American Edentates with "abnormal" vertebral articulations; the corresponding NOMARTHRA includes the Old-World forms. [Illustration] FIG. 90.--Right scapula and clavicle of Two-toed Sloth (_Choloepus hoffmanni_). x 1-2/3. _a_, Acromion; _af_, prescapular fossa; _c_, coracoid; _cl_, clavicle; _csf_, coraco-scapular foramen; _gc_, glenoid cavity; _pf_, postscapular fossa. (From Flower's _Osteology_.) Between the Sloths and Anteaters the extinct _Megatherium_ and some of its allies are to a certain extent intermediate. But it may be pointed out in the first place that there are certain important resemblances between the living forms. In both, retia mirabilia are developed in the tail (in spite of its reduction in the Sloths) and in the limbs. But, as is well known, retia are also found in other mammals far removed in the series from these under consideration. The reproductive organs generally are very similar, and they have both a dome-shaped and deciduate placenta. The latter character they share with the Armadillos and with the Aard Vark; _Manis_ having a non-deciduate placenta which is, like that of the Carnivora, zonary in form. The Edentates, at any rate the American forms, have a double vena cava posterior and no azygos vein. This condition is also met with among Whales.