THE IKTEBN Air SKELETON. 197 



toes only; those of the middle part of our foot answering to the 

 greater part of the skeleton of the bird's so-called "tarsus." 



The femur, or bone of the thigh, is more or less cylindrical 

 and expanded at either end. It is short and thick compared 

 with the tibia. Its upper end, or head, is rounded and is obliquely 

 directed inwards, its long axis being almost at right angles with 

 that of the shaft. It bears a deep pit into which a strong liga- 

 ment, the ligamentum teres, is inserted and helps to bind it to 



Fig. 158. 



Leg-bones op the Diver {Colymhus). 



/, Femur ; t, tibia ; ■p, cnemial process (only found thus developed in the 

 Diver and its allies) 5 6, fibula. 



the acetabulum. An upwardly projecting prominence from the 

 summit of the shaft is called the trochanter, and it plays against 

 the " antitrochanteric process " of the pelvis. On the back of 

 the femur, below its middle, there may be (as sometimes in 

 Swans and Ducks) a prominence into which the femoro-caudal 

 muscle is inserted. This may be called the inferior trochanter. 

 The distal end of the femur bears two prominences, or con- 



