70 



circular articular surface by which it was connected with the contiguous 

 sterna] rib. Purchased. 



409. A fragment of a sternal rib of the Mylodon robustus, showing a part of 

 the surface for articulation with an adjoining sternal rib. Purchased. 



410. A portion of another sternal rib, probably the last but one on the left side, 



of the Mylodon robustus, showing the sternal articulation, wdiich is 

 divided into three surfaces. Purchased. 



411. The sternal bone with which the preceding rib was articulated: it is pro- 



bably the penultimate one of the series, having the distal surface for the 

 succeeding sternal bone continuous with the two surfaces for the corre- 

 sponding sternal ribs. The distinction of the anterior and posterior parts 

 of the sternal bone is maintained at the upper end, which exhibits one 

 surface for the contiguous sternal bone, and four surfaces for the sternal 

 ribs. Purchased. 



412. The proximal end of the left humerus of the Mylodon robustus, showing 



the articular surface and the two tuberosities. 



The tuberosities, though not elevated so as to interfere with the rota- 

 tion of the head of the bone, as in the large ungulate quadrupeds, are 

 broad and well-defined. The rough deltoidal tract covers a great portion 

 of the fore-part of the shaft of the bone, from which it is separated by a 

 more or less prominent marginal ridge. The pectoral ridge is well- 

 marked. The musculo-spiral impression presents an unusual width and 

 depth. Purchased. 



413. The shaft and distal end of the right humerus of a Mylodon robustus ; the 



external supra-condyloid plate is broken off. The trochlear articulation 

 for the bones of the fore-arm indicates, by the regular convexity which 

 it presents to the radius, the free rotation of that bone. 



In its general characters the humerus of the Mylodon resembles that 

 of the Megalonyx and Megatherium ; but it differs in its greater strength, 

 the shaft being relatively much thicker with a stronger deltoidal plat- 

 form, and the proximal tuberosities larger and higher, particularly the ex- 

 ternal one. The humerus of the Mylodon differs in a more marked 



