3 2 



Physiology. 



2. The ends have smooth places, where they fitted other bones. 



3. Along the sides, especially near the ends, are ridges and projec- 

 tions, where the muscles were attached. 



4. There are small holes in the bone, where blood tubes passed in 



and out. 



5 . Saw a femur in two, lengthwise, and make 

 a drawing showing : 



(a) The central marrow cavity. 

 () The spongy extremities, noting especially 

 the directions of the bony plates and fibers. 



6. Observe the width of the lower end of 

 the femur, where it rests on the tibia. Sup- 

 pose these two bones were as narrow at their 

 ends, where they meet to form the knee joint, 

 as they are at their centers, what kind of a joint 

 would they make ? Illustrate by piling up a 

 number of spools on end ; the column is more 

 lightened than it is weakened by the hollow- 

 ing out of the sides of each spool. And the 

 central hollow of the spool does not greatly 

 weaken it. 



Joints. The ends of the bones, where they 

 fit together in the joints, are covered with a 

 layer of smooth, elastic, whitish or transparent 

 cartilage. The motion in the joints is made 

 still more easy by the synovia, resembling white 

 of egg. The ends of the bones are held to- 

 gether by tough bands and cords of ligament, 

 a form of connective tissue very much like ten- 

 don. Bones are closely covered by a tough 

 coat of connective tissue called the periosteum. 



All these structures can easily be found by 

 dissecting a sheep shank gotten from the 

 butcher, or in the hind leg of a rabbit. 



Fig. 2 1 . Action of the Mus- 

 cles in Standing. 



Standing. Although we are not ordinarily conscious 

 of the fact, when we are standing still we are using many 

 muscles. The accompanying figure illustrates how some 

 of the muscles act in keeping the body upright. Our 



