MAMMAL A, 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 male 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. (dd nat.) 
Distal end 
Tibia. of Fibula. Femur. 
i ' 
Entepicondylar Foramen. 
Radius. Ulna. 
Humerus. 
Hind-limb above. _ Fore-limb below. 
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. Lchidna 
may be about 16 to 18 inches long, with a fat compact 
