MAMMALIA. 



491 



Other skeletal peculiarities must be noted. The pelvis 

 bears a pair of epipiibic bones similar to those of the Meta- 

 t/ierla, and at least in Echidna the acetabulum is incompletely 

 ossified. The cervical ribs are incompletely fused on to the 

 cervical vertebrae, and the dorso-lumbar vertebrae have no 



Fig. 336 — DuCKMOLE {Ornithorhyiichtis anatinus). 



(From Gould's Mammals of Australia.) 



epiphyses, or only traces of them. The cranial bones anky- 

 lose early, obliterating all sutures,* and the rami of the 

 mandible are free. There is an entepicondylar foramen in 

 the humerus. 



The temperature of the body is low and inconstant. In 

 all these features the Prototheria show a low grade of struc- 

 ture approximating to the reptilian type. 



The young Ornithorhynchus is said to possess pre- and post-frontal bones. 



