i8 



PHYSIOLOGY. 



farther. It could not swing the weight outward, or push it upward. 

 But from the way in which the biceps is attached to the forearm, when 

 the muscle shortens an inch it may move the hand a foot. Of course 

 the hand moves much faster, and we have a great gain in speed by 

 reason of this lever arrangement. But we cannot lift so heavy a weight 



at this faster rate, as we could at the 

 elbow. For instance, suppose one were 

 to carry a heavy basket with a bail 

 handle by slipping the arm through 

 the bail up to the elbow. Now, it is 

 evident that the biceps is supporting 

 the weight. If it is as heavy as can be 

 held here, we know that we could not 

 hold the same weight in the hand with 

 the elbow bent at a right angle. 



Ball 



Articular Extremity 



Medullary Cavity 



- Hard Bone 



Study of One of the Long .. Bones. 

 For this, take, preferably, a femur 

 or a humerus. Let us suppose we have 

 a femur. 



1. Observe its shape, cylindrical, 

 somewhat curved, enlarged at the ends. 



2. The ends have smooth places, 

 where they fitted other bones. 



3. Along the sides, especially near 

 the ends, are ridges and projections, 

 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. Suppose 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 num- 



Fi* 7. 



Spongy Bone 



Articular Extremity 



Longitudinal Section of 

 Femur. 



