cannot be enumerated in a treatise like the present: suffice it to observe, that in the form of the skull, in the construction of the shoulder, and of the breast-bone, but particularly in the whole reproductive system of organs, the Monotremata present a manifest departure from a mammalian type, and a correspondent approach to that of the oviparous Vertebrata, tending to the Reptiles, more than to the Birds.
At the same time the preponderance of their organization shews, that notwithstanding their anomalies, they are truly Mammalia; and though they do not possess any external trace of an abdominal pouch, the presence of the marsupial bones in the skeleton, and many other details of their anatomy, sufficiently declare that their nearest affinities are with the Marsupiatia, of which they constitute the lowest and most aberrant type.
In these singular animals there are no true teeth, though one genus possesses horny substances in the jaw which represent those organs; the muzzle is produced into a long and flat beak, more or less resembling that of a duck; the eyes are small; the ears are merely minute orifices, destitute of external conch; the limbs are short and strong, adapted for digging; the feet have each five toes, furnished with stout claws, and on the hind feet is a sort of sharp spur, which has been supposed, but as it seems erroneously, to be a weapon of defence.
The order contains two genera, Echidna and Ornithorhynchus; both of which are confined to New Holland and Van Diemen’s Land.
