96 



the clavicular ligaments were doubtless attached to these and to the 

 contiguous concavities. The two posterior lateral margins present a nar- 

 row elongated slightly sinuous articular surface for the first sternal rib, 

 and, below this, a concavity forming the contracted posterior part of the 

 manubrium. The posterior boundary of the manubrium supports five 

 articular surfaces ; two on each side for the bifid, thickened, articular 

 ends of the second sternal ribs ; and the intermediate part by which it is 

 joined to the second bone, or the first of the series constituting the body 

 of the sternum. 



From the tertiary deposits of the Pampas of Buenos Ayres. 



Purchased. 



482. The sternal ends of the first pair of ribs, which were connected with the 



preceding manubrium sterni. 



The first rib increases in breadth as it approaches the sternum ; rough 

 prominences on its outer surface indicate where the ossified cartilage 

 originally began ; this, which in its present ossified and anchylosed state 

 forms the sternal end of the rib, was of a quadrate figure, broader than 

 long. It was articulated by a synovial surface of a narrow oval form to 

 the manubrium sterni. Purchased. 



483. The shaft and distal extremity of the humerus of a Mylodon, partly im- 



bedded in a mass of coarse limestone : the form of the distal articular 

 surface corresponds with that in the Mylodon robustus. The specimen 

 is from the same stratum and locality as the lower jaw of the Mylodon 

 Darwinii, viz. Bahia Blanca, near Patagonia. 



Presented by Charles Darwin, Esq., F.R.S. 



484. The head of the left femur, in the state of an epiphysis of the Mylodon 



Darwinii. 



From the cliffs at Bahia Blanca. 



Presented by Charles Darivin, Esq., F.R.S. 



485. The internal condyle of apparently the same femur of the Mylodo?i 



Darwinii. 



From the cliffs at Bahia Blanca. 



Presented by Charles Darwin, Esq., F.R.S. 



