VIII.] 



MARSUPIALTA. 



95 



Wombat {PJiascolomys vombatus) with 15, beir.g the only 

 known exceptions. The sternal ribs are articulated by 

 synovial joints with the sternum, but are not distinctly 

 segmented from the vertebral ribs, and are but feebly 

 ossitied by endostosis. There are no intermediate ribs. 



Fig. 44 — Sternum and ribs of the Great Armadillo [Priodontcs gi^as), \. 

 ps presternum ; xs xiphisternum. 



In the MoNOTREMATA the intermediate ribs are well 

 marked (see Fig. 43, p. 85), and only partly ossified by 

 endostosis, while the sternal ribs (except the first) are, 

 according to Parker, strongly ossified edosUaily, as in Birds. 

 The hinder sternal ribs are very broad and flat. The 

 Echidna h*as 16, and the Ornithorhynchus 17 pairs of 

 vertebral ribs ; they do not divide above into head and 

 tubercle, but are attached only to the sides of the bodies 

 of the vertebrae. 



