740 



MAMMALIA. 



Sub-Class PROTOTHERIA (Syn. ORNITHODELPHIA), 

 Orders Monotremata and (?) Allotheria 



The Monotremes include the duckmole (Ornithorhynchus 

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

 third form resembling Echidna, 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; Echidna 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 Echidna, 

 in a depressed area around 

 which a temporary pouch seems 

 to be developed. There are 

 no distinct mammae. 



The vertebral centra have 

 weak epiphyses in Ornithorhyn- 

 chus, and apparently none in 

 Echidna. In the duckmole the 

 post-sacral vertebrae 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 Echidna 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 



st. 



FIG. 402. Pectoral girdle 

 of Echidna. 



c., Scapula; cl., clavicle; i.cl., 

 prosternum or " interclavicle" ; co., 

 coracoid or metacoracoid; e.co.> 

 procoracoid or precoracoid ; st,^ 

 mesosternum. 



