114 



wards, the femur, viewed sideways, presents a double curve, like the italic /, 

 but is thicker at the two extremities than in the middle * . 



Patella f. — This is a comparatively large and strong triangular bone with 

 rounded angles : the base is uppermost and oblique ; the external surface mo- 

 derately convex, rough, longitudinally and coarsely striated, giving the appear- 

 ance of an ossified fibrous hgament ; the inner margin is longer and straighter 

 than the outer one, which is slightly concave. The internal or posterior surface 

 is traversed at its upper and broader part by the transversely oblong and bilobed 

 articular surface, which is convex transversely in the middle, and slightly con- 

 cave in the same direction at the sides : the inner lateral surface is the longest. 

 A narrow transverse strip of non-articular bone is situated above the articulation, 

 and a greater longitudinal extent of rough concave surface is continued below 

 that part to the obtuse apex, indicating the prolongation of the ossified sub- 

 stance into the short and strong ligamentum patellae. 



Tibia J. — If the femur of the Mylodon be remarkable for its shortness and 

 breadth, these proportions are exaggerated in the tibia, the breadth of the upper 

 extremity of which exceeds three-fourths of the length of the entire bone. The 

 shaft is more flattened than the femur in the antero-posterior direction, but is as 

 strongly marked by muscular ridges and Ugamentous grooves. The upper or 

 proximal surface of the tibia§ is horizontal, and presents a reniform figure, con- 

 cave posteriorly, and with a small notch at the middle of the anterior convexity ; 

 it supports two articular surfaces, separated by a depression corresponding with 

 , the intercondyloid groove in the femur. The outer surface (6) is the smallest, 

 and has a nearly circular figure ; it is very shallow, and occupies the posterior 

 half of the external moiety of the head of the tibia, the anterior portion of the same 

 moiety being rough and irregular, partly convex, partly concave, and perforated 

 by vascular foramina. The inner surface (a) is elliptical, and occupies the whole 

 of the corresponding division of the head of the tibia : a small portion of its an- 

 terior part is convex, and rises to a slight eminence near the middle excavation ; 

 the rest of the surface is slightly concave. The part of the tibia which supports 

 the articular surface for the external condyle is produced backwards, in the 

 form of a thick horizontal platform of bone overhanging the shaft. A small 



* Plate XIX. t Plates XVII. and XVIII. fig. 2. The bone is figured upside down, 



t Plate XIX. fig. 4. Plate XX. figs. 1. 2, 3, 4. § Plate XX. fig. 3. 



