CHARACTERS OF PROTOTHERIA. 



68i 



Sub-class Prototheria (Syn. Ornithodelphia), 

 Order Monotremata. 



This sub-class includes the duckmole {Ornithorhyiichus 

 anatinus), the spiny ant eater {Echidna acukata), and a 

 third form resembling Echidna, but often referred to a 

 distinct genus as Proechidna. These are the lowest Mam- 

 mals, and exhibit affinities with Sauropsida, and perhaps 

 even with Amphibia. It need hardly be said that they 

 have no special affinities with Birds. 



General Characters of Prototheria. 



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 Pro- 

 echidna, 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 tem- 

 porary pouch seems to be 

 developed. There are no 

 distinct mammae. 



The vertebral centra bear 

 no epiphyses. The skull is 

 smooth and polished as in Birds, for the sutures disappear. 

 The rami of the lower jaw do not unite in front, and 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 is long 

 and not fused to the centrum. The (meta-) coracoids reach 

 the prsesternum, there are also large epicoracoids and a 

 T-shaped interclavicle, the whole girdle resembling that of 

 Lizards. An interclavicle is, however, recognisable in he 



Fig. 243. — Pectoral girdle of 

 Echidna. ( From Edinburgh 

 Museum of Science and Art. ) 



Sc.^ Scapula; cl., clavicle; i.cL, inter- 

 clavicle ; CO., metacoracoid ; e.co., epicora- 

 coid ; St., sternum. 



