80 HITCHCOCK'S ANATOMY 



gression, and also for affording a firm support to the trunk 

 when engaged in the various kinds of labor. Were these ex- 

 tremities much shorter than they now are, walking would not 

 only be a tediously slow process, but a laborious one. The 

 femur has some remarkable peculiarities. In the first place 

 it presents in its articulation with the innominatum the most 

 perfect specimen of a ball and socket joint in the system. 

 Besides this it bends at nearly a right angle at its upper end, 

 making what is called the neck, and here it is that the frac- 

 ture of the thigh-bone generally occurs. The use of this 

 curvature is to place the points of support for the trunk as 

 far as possible from the center of gravity of the body, thereby 

 giving the body the most secure position on the lower ex- 

 tremities, and especially for the attachment of powerful 

 muscles to move the thigh and leg, as well as to maintain 

 securely the trunk when the legs are the fixed points. This 

 projection is called the Trochanter process, and is spongy or 

 cellular in its structure. And it is not a little interesting to 

 notice, when this process is sawn through in a perpendicular 

 direction, that the cells are arranged in an arched form from 

 below upwards, thereby greatly aiding the strength of the 

 bone. The same arrangement is seen in some other bones of 

 the body, when they are in an exposed position. The lower 

 extremity of this bone, as has already b.een mentioned, is 

 greatly expanded, in the shape of two condyles for the firm 

 articulation with the tibia. The necessity for this lies in the 

 fact that the knee-joint is one of the most exposed joints in 

 the whole body, and the one which receives the hardest strain. 

 The protection of the nerves and blood vessels, which are sent 

 to the leg, is also worthy of a notice. It is effected by a 

 deep groove between the condyles on the backside of the 

 leg, which guards these vessels from blows in every direc- 

 tion except behind, from whence they are the least apt to come. 



What remarkable joint between the femur and the innominata? What is the ar- 

 rangement of the cellular structure in the upper part of the femur? Why has the fe- 

 mur so large processes on its lower extremity ? 



