In the skull there is a complete though slender zygoma; the premaxillaries, though small, are not so rudimentary as in the American Edentates. The annular tympanic is not ankylosed to the surrounding bones, a character found in other low mammals. Contrary to what is found in Manis, Orycteropus has a huge lachrymal. There are thirteen dorsal and seven lumbar vertebrae. The clavicle is well developed. Orycteropus is peculiar among Edentates in that the ischia do not unite with the vertebral column. The femur has a third trochanter.
As mentioned on p. [162], the Aard Vark is diphyodont like normal mammals. The permanent teeth consist of five molars and premolars on each side of each jaw; the first two of these are premolars, and are simpler in their form than the succeeding two teeth, which are partly divided by a median furrow into two halves. These teeth are also peculiar in that they consist entirely of vaso-dentine. They have been compared in minute structure to those of the Ray Myliobates. According to Mr. Oldfield
Thomas[[109]] there are seven milk teeth on each side of the upper jaw (limited to the maxillae, and thus not incisors). An eighth tooth was discovered on one side of one of the specimens examined by Thomas. In the lower jaw there are only four milk teeth on each side. It is interesting to note that the histological structure of these milk teeth agrees with that of the permanent teeth. There are two species of this genus found in Africa: the southern, O. capensis, is more hairy than the northern, O. aethiopicus. O. gaudryi is a Pliocene species from the Island of Samos and from Persia, described by Dr. Forsyth Major and Dr. Andrews.[[110]] It closely resembles the existing O. aethiopicus.
Fig. 108.—Section of lower jaw with the teeth of Orycteropus. × 2. (After Owen.)
Of the Scaly Anteaters, Group Squamata or Manidae, there is really but one genus, though Phatagin, Pholidotus, Smutsia, and Pangolin have been used to distinguish various forms. The genus Manis is African and Oriental in range. Dr. Jentink, who has lately revised the species, allows seven.[[111]] The external form of these animals is fairly well known, the remarkable scales distinguishing the Pangolins from other animals. Between the scales lie hairs, which seem to be absent in the adults of the African species, though present in the young, thus affording a convenient method of distinguishing the Ethiopian from the Oriental forms. The scales have been compared to agglutinated hairs. That they are not "merely mimetic of the Lizards' scales" is held by Weber,[[112]] who compares them directly with those
structures, as he does the scales of other mammals, such as those upon the tail of Anomalurus, etc. This, however, is not a universal opinion. It is true that these scales occur chiefly in the lower forms of mammals such as those under consideration, Marsupials, Rodents, and Insectivores; but the fact that the hairs are developed before the scales shows, or seems to show, that the former are the older structures, and to lead to the inference that the scales of mammals are new structures. The scattered hairs of the Pangolin have no sebaceous glands excepting on the snout. This, again, looks as if they were degenerate structures, and emphasises the non-archaic character of the scales. These animals have no trace of teeth except possibly some slight epithelial thickenings which have been interpreted as a last remnant; the tongue is suited for the capture of ants, and is therefore much like that of the not nearly-related American Anteaters. The stomach is of simple form; it is characterised by a large gland, which suggests that of the Koala (see p. [144]); the intestine has no caecum. Retia mirabilia occur on the limb arteries. The placenta is non-deciduate and diffuse; it is specially compared by Weber with that of the Horse. Considering the many adaptive resemblances between this genus and the American Anteaters, especially in the mouth cavity, it is remarkable that in Manis the pterygoids are not joined as they are in Myrmecophaga. In spite of statements to the contrary, it appears that there is sometimes a distinct lachrymal.
A remarkable feature in the skeleton of Manis is the singular sternum. The xiphoid cartilage is extraordinarily elongated into thin strips, which reach the pelvis and return. This state of affairs is to be found in the African species only. This structure is not comparable, as it has been said to be, with abdominal ribs such as those of the reptile Hatteria.
These animals are mainly anteaters. The Japanese have a curious legend as to the method adopted for the capture of ants, which is related by Dr. Jentink in his monograph of the genus. The Manis "erects his scales and feigns to be dead; the ants creep between the erected scales, after which the anteater again closes its scales and enters the water; he now again erects the scales, the ants are set floating, and are then swallowed by the anteaters"! The same story is related by Mr. Stanley Flower on the authority of the Malays.
Though it seems clear that the likenesses which Manis shows