MAMMALIA. 



493 



to ten in all. They appear to have two main cusps and 

 smaller " crenulations, " the cusps lying externally in the 

 lower jaw and internally in the upper. The beaks are borne 

 upon bony processes of the premaxilla and the skull of the 

 duckmole is at once recognised by the peculiar " beak- 

 shape " of the facial region, together with the hard cornules. 

 The m.ale Ornithorhynchus has a " spur " on the inside of 

 the hind-foot which is traversed by a canal continuous with 

 the duct of a gland situated over the thigh. It is probably 



Fig. 338. — Bones of Limbs of Ornithorhynchus. {Ad nat.) 



Tibia. 



Distal end 



of Fibula. 



Femur. 

 I 





'X 





Radius. Ulna. 



Hind-limb above. Fore-limb below. 





Humerus. 



a poison-apparatus and is supposed to be functional early in 

 the breeding season. It is rudimentary in the young female. 

 The skeleton of the limbs shows powerful ridges and crests 

 on humerus and femur, and the fibula has a projecting 

 process beyond the knee-joint which gives it a deceptive 

 resemblance to an ulna. 



Echidna and the allied genus Proechidna, the ^^ Porcu- 

 pine anteaters," are, like Ornithorhynchus, confined to the 

 Australian region, Proechidna to New^ Guinea. Echidna 

 may be about 16 to 18 inches long, with a fat compact 



