566 MAMMALS. 



Sub-class Prototheria (Syn. Ornithodelphia), 

 Order Monotremata. 



This sub-class includes the duckmole {Ornithorhynchus 

 anatinus), the spiny ant-eater (Echidna aculeatd), and a 

 third form resembling Echidna, but often referred to a 

 distinct genus as Froechidna bruignii. These are the lowest 

 Mammals, and exhibit affinities with Sauropsida, and perhaps 

 even with Amphibia. It need hardly be said that they 

 have no special affinities with Birds. We have already 

 contrasted them with the other Mammals, but may again 

 state their more important characteristics. 



General Characters of Prototheria. 



The duckmole is found in the rivers of Australia and 

 Tasmania; Echidna, in Australia, Tasmania, and New 

 Guinea ; Froechidna in New Guinea. 



In Ornithorhynchus, the skin is covered with soft fur ; in 

 Echidna and Froechidna, there are spines among the hairs. 

 The mammary glands in the female Ornithorhynchus open 

 on a flat patch; in Echidna, in a depressed area around 

 which a temporary pouch seems to be developed. 



The vertebral centra bear no epiphyses. The skull is 

 smooth and polished as in Birds, for the sutiires of the 

 bones do not persist. The rami of the lower jaw do not 

 unite in front, and they have no ascending process. In 

 Ornithorhynchus, there are true mammalian teeth, but only 

 in the young ; in Echidna, none are present. Cervical ribs 

 remain distinct for a time at least; the odontoid process 

 of the second vertebra or axis is long and not fused to 

 the centrum. The coracoids reach the prsesternum, there 

 are large epi- or pre-coracoids and a T-shaped interclavicle, 

 the whole girdle resembling that of Lizards. In Orni- 

 thorhynchus, the ischia form a long ventral symphysis; in 

 Echidna, the acetabulum socket for the femur is incompletely 

 ossified as in Birds ; the pubes bear epipubic bones, as in 

 Marsupials. On the side of the tarsus, in the duckmole, 

 there is a spur perforated by the duct of a gland. This 

 spur persists in the males, is rudimentary in the females. 

 The male Echidna has a similar but smaller spur. 



