86 LAND MAMMALS IN THE WESTERN HEMISPHERE 



on the posterior side two large, rounded prominences, the 



condyles, which articulate with the shin-bone to form the 



knee-joint. On the anterior side is a broad, shal- 



11 low groove, the rotular groove, in which glides 



*^ the patella, or knee-cap. The patella is a large 

 ossification, of varying shape, in the tendon com- 

 mon to the four great extensor muscles of the 

 thigh, the action of which is to straighten the leg. 

 "*"" ■ The lower leg, like the fore-arm, has two 



f-rf bones, which, however, are always parallel, never 

 int'ron. crossed, and have no power of rotation. Of 



Fig. 36. —Left fe- ^j^ggg ^j^g inner One is the shin-bone, or tibia, 



mur of Wolf, in- ' ' ' 



side of lower end. which is always the larger and alone enters into 



ext. con., external ,i ^ • ' j. rni j. i !_ ■ xi_ ^l t 



condyle, int. the knee-joiut. The external bone IS the ^oma, 



con., internal which is almost entirely suppressed in certain 



uTar groove, highly Specialized forms, such as the horses and 



Above, are two ruminants, the tibia carrying the whole weight. 



views of the left ''. ii.i .,.. , i 



patella, anterior Thfe Upper end of the tibia IS enlarged and ex- 



and internal ^gj^^jg ^.^gj, ^Jj^^^ ^f ^]^g ^y^^^^ . J^ J^^g ^.^^ slightly 

 sides. 



concave surfaces for articulation with the con- 

 dyles of the femur, the approximate edges of which are raised into 

 a bifid spine. The upper part of the shaft is triangular, with one 

 edge directed forward, and the superior end of this edge is rough- 

 ened and thickened to form the cnemial crest, to which is at- 

 tached the patellar hgament. The middle portion of the shaft is 

 rounded and the lower end broad and usually divided by a ridge 

 into two grooves or concavities for the ankle-bone ; from the in- 

 ner side of this end projects downward a tongue-like process, the 

 internal malleolus, which prevents inward dislocation of the ankle. 

 The fibula is relatively stoutest in the less advanced mam- 

 mals and is usually straight and slender, with enlarged ends, 

 the lower one forming the external malleolus, which serves to 

 prevent outward dislocation of the ankle. In many forms 

 the fibula is coossified with the tibia at both ends, and in the 

 most highly specialized hoofed animals, such as the horses. 



