XVIII.] GENERAL CHARACTERS. 299 



called condyles (Fig. 109, ec and ic). The slightly elevated 

 roughed portions of bone above the articular cond3les are 

 termed the tuberosities. 



The femur has a main centre of ossification for the shaft, 

 and epiphysial centres for the head, for each trochanter, and 

 for the lower extremity. (See Fig. 109.) In most Mammals 

 the great trochanter and head coalesce together before they 

 join the shaft. The lower epiphysis is the last to become 

 united. 



The skeleton of the second segment of the limb consists 

 of two bones, the tibia and fibula} of which the former 

 is the larger in all Mammals. These bones always lie in 

 their primitive, unmodified position, parallel to each other, 

 the tibia on tlie preaxial, and the fibula on the postaxial 

 side, and are never either permanently crossed or capable 

 of any considerable amount of rotation, as in the corre- 

 spondmg bones of the fore limb. In the ordinary walking 

 position the tibia is internal, and the fibula external. 



The tibia has an expanded proximal end, with a flat- 

 tened articular surface, divided into two slightly concave 

 focets, by a rough median eminence, to which the intra- 

 articular or crucial ligaments of the knee-joint are attached. 

 I'he shaft is usually more or less trihedral, with one fiat 

 surface directed backwards, and one border forwards. The 

 upper end of this border is thickened into a rough tuberosity, 

 into which the tendon of the great extensor muscles of the 

 leg are inserted. The lower end is slightly expanded, and 

 has a somewhat square articular surface to receive the proxi- 

 mal bone of the tarsus, or astragalus. The inner (or pre- 

 axial) side of the bone is prolonged beyond this surface, 

 forming a process called i}iter?ial malleolus, which is applied 



^ Also occasionally called pcronc, whence "peroneal," applied to 

 structures in relation w ith it. 



