Mr. Clift on the Megatherium. 445 



Ribs. 



The first is nearly straight, and is enlarged and flattened at tlie sternal extremity. 



Ft. In. Lines. 



It measures in length 1 2 



Breadth of the vertebral end 3 9 



Breadth of the sternal end 3 1 



Greatest breadth of the rib near the sternal end 4 7 



Least circumference 4 8 



Greatest circumference 11 



The length of the longest rib following its outer curvature 3 6 



From the tubercle to the head of rib 6 



Greatest breadth 3 6 



The true ribs which join the sternum (except the first and last) have a double articular surface 

 at the sternal end, each of which is adapted to two contiguous portions of the sternum*. 



Sternum. Ft. in. Lines. 



The manubrium sterni, or first bone of the sternum, measures in length 9 

 In breadth 6 8 



It has only three articular surfaces ; two for the sternal ends of true ribs, 

 and one for the adjoining bone of the sternum ; but it is probable that the 

 clavicles were united by ligaments to the shallow cavities on the inner surface 

 of the manubrium^ above those for the ribs. 



The next bone of the sternum, in the specimen^ is very remarkable for the 

 number of its articular surfaces, there being no fewer than ten, viz. one on 

 the anterior and one on the posterior surface for its union with the other 

 bones of the sternum, and four on each side for the double articular surfaces 

 at the sternal ends of the ribs. 



Ft. In. Lines. 



This bone measures : In length 2 6 



In breadth 4 3 



Antero-posterior diameter .... 3 



The third bo7ic of the sternum in this collection is not the third in natural juxta-position, but 



appears to be the last, for it has but one articular surface for the sternum, and only two inferior 



costal surfaces (the two being blended together on each side) ; but there are, as in the preceding, 



four on the upper part. 



Ft. In. Lines. 



Its length 2 9 



Breadth 3 4 



Antero-posterior diameter 3 3 



* Most, if not all, of the true ribs had bony articulations to the sternum in lieu of cartilaginous 

 extremities, and a joint at the part where the rib usually terminates and the cartilage begins in 

 most other quadrupeds. 



VOL. III. SECOND SERIES. 3 M 



