THE SKELETON. 67 



The greater trochanter projects from the proximal end of 

 the bone to a level with the head. On this process are 

 inserted the pyriformis, gluteus medius, and gluteus mini- 

 mus muscles, all of which originate on the innominate bone. 

 The. lesser trochanter is the small projection on the caudal 

 aspect of the proximal portion of the bone (Fig. 40). The 

 intcrkro chant eric ridge or posterior intertrochanteric line 

 extends between the two trochanters, and lying between 

 this line and the neck is the digital fossa. The external and 

 internal condyles are the articulatory processes on the distal 

 end of the bone. The blunt projections at their roots are 

 the external and internal tuberosities. The inter condyloid 

 notch forms the depression on the caudal aspect between 

 the condyles. On the cranial aspect is the trochlear sur- 

 face for articulation with the patella. Two small sesamoid 

 bones, the fabellae, are present on the caudal aspect of the 

 condyles, but they are usually removed in preparing the 

 skeleton. The linea aspera is the slightly roughened line 

 beginning on the caudal side, distal to the middle and ex- 

 tending proximally a short distance, where it bifurcates. 



The form of the femur varies but little among mammals 

 having functional posterior limbs. No living Sirenia have 

 any trace of a femur, but a vestigial femur is present in 

 Halithcriuni, a fossil form. The hind-limbs are wanting 

 among the Cetacea, but in a few forms nodules of bone or 

 cartilage may represent the femur. In most Perissodactyla 

 and Rodentia, and in some Insectivora and a few fossil 

 Carnivora, a third trochanter is present. 



The patella, or knee-cap (Fig. 21), is a sesamoid bone 

 developed in the tendon of the quadriceps extensor muscle 

 (Fig. 52). It is somewhat the shape of an almond and 

 about half its size. It articulates with the trochlea of the 

 femur. 



The tibia is the larger bone of the crus. It presents two 



