MONOTREM'ATA (Gr. monos, single, trema, an opening), the lowest order of mam Inaba, in many of their characteristic points indicate an approximation to birds. Time skull is smooth; the brain-case very small as compared to the face; the smolt much pro longed, and the jaws unprovided with soft movable lips, and not furnished with teeth. (In the ornithorhynchus there are two horny plates in each half-jaw, which act as teeth, while in the echidna even these substitutes for teeth are wanting.) The cranial bones coalesce, as a bird's, at a very early period, and leave no signs of sutures. The external ear is altogether absent; while the eyes, though small, are perfectly developed.
The bones of the shoulder, forming the scapular arch, are unlike those of ally other mammals, and in some respects resemble those of birds, and in other re pests those of reptiles. At the top of the sternum is a T-shaped bone, formed by the union of the two clavicles, corresponding to the furealum in the bird's skeleton. The corncob] bones, which iu other mammals are mere processes of the scapula, mime here extremely large, and assist, as in birds, in strengthening the scapular arch; while the scapuhe it mselves are produced beyond the socket of the humerns (the glenoid cavity), to as to articulate with the sternum.
The pelvis is provided with marsupial bones, although these animals do not possess a pouch.
The feet have five toes, armed with long nails; in addition to which, the hind-feet of the males are provided with a perforated spur-like weapon, which is connected with a gland. The Australian aborigifies believe the wounds made by this spur to be poison ous; but there is no scientific evidence of the fact.
Time ovaries are analogous to those of birds, the right ovary being comparatively unde veloped, while the left forms a racemiform mass. The orifices of the urinary canals, the intestinal canal, and the generative canal. open, as in birds, into a common cloaca, from which circumstance the order Monotrenzata derives its name. The mammary glands, of which there is only one on each side, are not provided with nipples, but open by simple slits on each side of the abdomen.
This order includes only two or three species, all natives of Australia or Van Die men's Land, which, however, form two families—the ornithorhynchidee (see DUCK-BILL), and the eckidnkke (see ECHIDNA), No fossil remains of any animals of this order have as yet been discovered.