740 MAMMALIA. 
Sub-Class PROTOTHERIA (Syz. ORNITHODELPHIA), 
Orders Monotremata and (?) Allotheria 
The Monotremes include the duckmole (Ornithorhynchus 
anatinus), the spiny ant-eater (Echidna aculeata), and a 
third form resembling Zchidna, but often referred to a 
distinct genus as Proechidna. These are the lowest 
Mammals, very different from all the rest, and they exhibit 
affinities with Reptiles. 
The duckmole is found in the rivers of Australia and 
Tasmania; Zchidna in Australia, Tasmania, and New 
Guinea; Proechidna in New 
Guinea. 
In Ornithorhynchus the skin 
is covered with soft fur; in 
Echidna and Proechidna there 
are spines among the hairs. 
The mammary glands in the 
female Ornithorhynchus open 
on a flat patch; in Zchidua, 
in a depressed area around 
which a temporary pouch seems 
to be developed. There are 
no distinct mamme. 
: p The vertebral centra have 
sc., Scapula; cé., clavicle; z.cé., : : - 
prosternum or “‘interclavicle” ; co., weak epiphyses in Ornithorhyn- 
coracid of metacoracid:, ¢ce chus, and apparently none in 
Pecotemm, ° “Echidna. In the duckmole the 
post-sacral vertebrze are stronger 
than the pre-sacral. The skull is smooth and polished as in 
Birds, for the sutures disappear. The rami of the lower jaw 
do not unite in front, have no ascending process, and have a 
slightly inflected angle. In Ornithorhynchus there are true 
mammalian teeth, but only in the young; in ZAchidua none 
are present. Cervical ribs remain distinct for a time at least ; 
the odontoid process of the second vertebra is for a long 
time free from the centrum. Except on the atlas of 
Echidna, the cervical vertebrae are without zygapophyses 
or articular processes. The (meta-) coracoids reach the 
sternum; there are also large precoracoids (often called 
epicoracoids, but homologous with the precoracoids of many 
Fic. 402.—Pectoral girdle 
of Echidna. 
