In the skull the Echidna differs from Ornithorhynchus in the greater extension backwards of the palatines, and the larger size of the pterygoids. The extent and relations of these bones to each other is not at all unlike that which obtains in many Whales. The premaxillae show traces of the same divergence followed by convergence of their ends that is seen in the Platypus. There are only sixteen pairs of ribs, and either three or four lumbar vertebrae. Echidna has no trace of teeth, and there are no horny pads which take their place; the mouth is as edentulous as in the true American Anteaters. The brain (Fig. 53) is marked by sulci, contrary to what we find in Ornithorhynchus. The genus has been divided into three species, but it is doubtful whether more than one can be allowed, which ranges from Australia through the Papuan region. While there is but one species of true Echidna, a New Guinea species must clearly be referred to a distinct genus Proechidna.[1] This animal is to be distinguished by the fact that there are usually but three toes on each foot. But there are copious rudiments of the other phalanges, upon which claws are sometimes developed. The beak is curved downwards, and the back is rather arched; the whole animal has the most singular likeness to an Elephant! The ribs are increased by one pair, and there are four lumbar vertebrae. The one species is named P. bruijnii. The Hon. W. Rothschild[2] distinguishes a form P. nigroaculeata, which is allowed by Mr. Lydekker.
Fig. 54.—Australian Anteater. Echidna aculeata. × 1⁄6.
