34 TRANSACTIONS OF THE WAGNER FREE 



which is Hke that of Mylodon robustus, as represented in the same work. 

 The breadth of the articulation is 130 mm. 



The tibia, of which a representation is given in figure i, plate V., also 

 closely resembles that of the Mylodon robustus, both in its form and propor- 

 tions, as given in Prof Owen's figures, plate XX., of the work above 

 mentioned. It is a short, exceedingly robust bone, the breadth of the proxi- 

 mal extremity being upwards of three-fourths its length. The shaft, 

 compressed cylindroid and expanding towards the extremities, at its nar- 

 rowest part is nearly twice the width transversely that it is fore and aft. The 

 proximal surface, reniform in outline, exhibits the usual pair of articular 

 surfaces. Of these, the outer, very much the larger, is oval and deeply con- 

 cave, with its longer diameter directed obliquely from before inward and 

 backward. The outer articular surface, nearly plane except a small portion 

 behind, is half circular outwardly and forms two sides of a square inwardly. 

 The patellar tubercle is a thick triangular eminence bent outwards. Beneath 

 the tuberosity supporting the outer condylar surface is that for the fibula ; 

 a large elliptical plane sloping from without inward and backward and 

 looking downward, and surrounded with a thick rugged border for liga- 

 mentous attachment. 



The distal extremity of the tibia presents the articular surface of the 

 ankle-joint divided into three portions, of which the inner two are for the 

 astragalus, and the third, smallest, outer, half circular one for the fibula. Of 

 the astragalar articulation the inner division is a deep, half conical, concave 

 recess ; the outer a wide, reniform, nearly flat or slightly concave surface. 



The internal malleolus presents a deep, wide groove descending obliquely 

 from the back of the shaft forward for the flexor and adductor tendons of 

 the foot. The outer part of the distal extremity forms a thick, rough 

 tuberosity for ligamentous attachment with the fibula. 



The measurements of the tibia are as follows : 



Extreme length along the inner border, • . 



Length along the fibular border, . . . . 



Breadth of proximal extremity, ..... 



Longer diameter of the inner condylar articulation. 



Shorter 



Transverse diameter of outer articulation. 



Fore and aft " " "... 



Extreme breadth of distal extremity. 



Greater " " " fore and aft, 



Breadth of distal articulation transversely, 



fore and aft, . 

 Greater breadth of upper fibular articular surface, . 

 Smaller " 



• 233 



mm 



. 183 





. 180 





95 





. . 87 





72 





. 70 





144 





. 100 





123 





. 92 





64 





. 34 





