25.| THE SHOULDER GIRDLE. [CHAP. 



articulates to the side of the presternum, just in front of the 

 first rib. 



Placed in front of the inner end of the coracoid is a 

 broad, flat, shield-like plate of bone (epicoracoid, ec Fig. 84, 

 Prc, Fig. 85), the rounded inner border of which passes 

 beyond the median line, overlapping the corresponding bone 

 of the opposite side. In the Echidna the left lies superfici- 

 ally to the right, while in the Ornithorhynchus this disposition 

 is reversed. 



Upon the front end of the presternum, lying below its 

 anterior continuation (proosteon, see p. 104) and also below 



FIG. 85. Ventral view of shoulder-girdle and anterior portion of sternum and 

 sternal ribs of Ornithorhynchus (O. ^anatinns) ; . sc scapula; cl calvicle ; 

 c coracoid ; Prc epicjracoid ; Kp interclavicle or episternum. 



the epicoracoids, is a large azygous T-shaped bone (ic Figs. 

 84 and 44 ; Ep Fig. 85), which has no homologue in any 

 other Mammal, called interclavicle or episternum. Its lower 

 end is broad, and rests on the expanded straight upper 

 margin of the presternum ; it contracts somewhat above 

 before dividing into a pair of nearly horizontal, slightly-curved 

 arms, which extend outwards towards, though not quite 

 reaching, the acromion. This bone differs from the pre- 

 sternum, and the small proosteal plate behind its lower 



