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 
intertrochanteric 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 intercondyloid 
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 fabellz, 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 
Halitherium, 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 
