VII.] 



EDENTATA. 



85 



but very narrow below ; and, according to Prof. Parker, each 

 ossifies from eleven centres. They are connected by syn- 

 ovial joints to each other, and to the strongly ossified sternal 

 ribs, which have broad, sub-bifid heads. The xiphisternum 

 expands posteriorly into a wide cartilaginous flap. 



In the Sloths the sternum is long and narrow. The Three- 

 id species (Bradypus) have a rather broad presternum, but 

 rith no prolongation in front of the attachment of the first 



FlG. 43. — Sternum and adjacent parts of the skeleton of a young Ornithorhynchus 

 (O. paradoxus), c clavicle ; ic interclavicle , po pro-osteon (a part of the true 

 sternum) ; ps presternum ; ms mesoaternum ; sr sternal ribs ; ir intermediate ribs ; 

 vr vertebral ribs. 



rib. This is followed by eight small mesosternal segments, 

 and a very small rounded xiphisternum. In the Two-toed 

 Sloths (Choiapus), the presternum is narrow, slightly keeled, 

 and forms a considerable projection in front of the attach- 

 ment of the first rib. The mesosternum has twelve seg- 

 ments, and the xiphisternum is rudimentary or absent. 



