338 A NEW MYLODON. 



considerably more compressed instead of being nearly the width of the articular 

 head. The distal condyles are of about the size of those in the South American 

 species, but in end view the concavity at the knee for the reception of the patella 

 and its ligaments, is much flatter and apparently a little broader. The femur 

 presents the following measurements: — , 



Antero-posterior diameter of proximal condyle, circa 125 mm. 



Lateral diameter of same 118 



Depression for ligamentum teres, base, 38; height, 58 



Breadth of femur across middle of shaft 1 65 

 Width of articular surface for patella (anterior face of knee) 107 



Greatest width across distal condyles (posterior view) 198 



Greatest width of outer posterior condyle 68 



Greatest vertical height of same 58 



Greatest width of inner posterior condyle 82 



Greatest vertical height of same 97 



Ventral width of isthmus between distal condyles 58 



The patellae are almost squarely truncate across the top, but at the outer 

 upper corner are bordered by a thick ridge of bone that projects above the general 

 dorsal outUne. Ventrally the sides of the bone converge to a blunt point. 

 In M. robustus there is a raised portion of bone visible along the entire^dorsal 

 edge of the articular facet, as seen in posterior view. This facet is of different 

 shape in the two patellae of the specimen studied. In one it is slightly narrower 

 and longer than in the other, 39 to 44, and 113 to 102 in comparative diameters. 



The remarkably short and broad tibia is nearly identical with that of the 

 South American Mylodon. That of the left side measures in extreme length 

 between uprights 255 mm.; in extreme breadth across the proxmial facets, 171 

 mm. The broad thick shaft contracts to a width of 100 mm. at the middle 

 and expands distally to 131 mm. across the malleoli. Of the two articular 

 facets at the proximal end, the external has a practically fiat surface, separated 

 by a depression from the slightly hollowed and larger internal facet. The long 

 axes of both are nearly parallel and at about 45 degrees to an antero-posterior 

 line. In M. robustus the smaller facet is of shghtly more oval outline with its 

 axis nearly at right angles to that of the larger. These pecuharities are no doubt 

 subject to much individual variation. The outer facet is the upper surface of 

 a projecting shelf whose lower portion forms an articulation for the proxmial 

 end of the fibula, of roughly elliptical outline, transversely placed. The inter- 

 nal malleolus at the distal end of the tibia is shghtly less expanded than in 



