62 GENERAL STEUCTURE OF FEET. 



tance from the body. They spend most of their 

 time, and find the whole or nearly the whole of 

 their food, in the water ; and such of them as have 

 not the power of flight (for some of them are so ex- 

 clusively aquatic that they can neither fly in the air 

 nor walk on the earth) deposit their eg-gs near the 

 margin of the water, so that their terrestrial opera- 

 tions are limited to shuffling along a few feet, or 

 sitting erect upon the rocks, in which latter, and even 

 in the former, the tail assists in supporting them, as is 

 the case with beavers when they stand up. 



The head of the femur is articulated rather farther 

 forward in walking birds than in the mammalia; 

 and the femur itself is not so free or so much used 

 in the motion of the leg. The tibia, or true leg, is 

 the part usually called the thigh, or in the larger 

 birds, which are brought to table, the drum-stick. 

 In birds which make much use of their feet, the tibia 

 is much loaded with muscles ; and it is generally 

 protected by a profusion of soft and downy feathers, 

 especially in those birds which are much exposed to 

 the weather, and use their toes in clutching or killing 

 their prey. 



Many of the wading birds, and some of the running 

 ones, have a portion of the under end of the tibia 

 bare of feathers ; but the muscles do not descend so 

 low as that part ; and it may be considered as a 

 general arrangement in the structure of birds that the 

 muscles are always under a protecting covering of 

 feathers. 



The tarsi and toes, and also the naked portions of 

 the tibia, contain few or no muscles, but are made up 

 of bones, tendons, straps of ligaments for keeping 

 the tendons in their places, and the integuments, 

 which are verv firm and tough skin, variously covered 



