XIV.] 



MONO TREMA TA . 



26' 



the supposed primitive trihedral rod being flattened in 

 opposite directions. In the Cetacean scapula there are two 

 nearly parallel surfaces, the postscapular and the subsca- 

 pular fossae ; while the third, the prescapular fossa, is reduced 

 to the smallest possible width quite obsolete, in fact in 

 Platanista. In the Monotreme the last-named fossa is so 

 expanded that the other two, instead of being parallel to 



Pf 



1C 



FIG. 84. - Side view of right shoulder girdle of a young Echidna {Echidna hystrix), ^ 

 ss suprascapular epiphysis ; ssf subscapular fossa ; pf postscapular fossa ; cb 

 coracoid border ; gb glenoid border ; ^ spine ; a acromion ; ess coraco-scapular 

 suture ; gc glenoid cavity ; c coracoid ; ec epicoracoid ; cl clavicle ; ic interclavicle ; 

 ps presternum. 



each other on opposite sides of the bone, are brought almost 

 into one plane, which is parallel and opposite to the sub- 

 scapular fossa. 



The coracoid (c) is a stout subcylindrical bone, expanded 

 at its extremities, taking at its upper end a considerable 

 share in the formation of the glenoid cavity, and becoming 

 firmly ankylosed with the scapula. At its lower end it 



