THE HUMAN BODY AS A MACHINE 223 



skull ; and the appendicular, of the appendages or parts attached 

 to the main axis. Which part is composed of the greater num- 

 ber of bones ? 



2. Note that the spinal column is composed of many single 

 bones (vertebrae). Are they immovable, or flexibly arranged? 



3. How many ribs do you find ? Are they all alike ? 



4. Where are the ribs fastened ? 



Conclusions. 1. What seems to be the uses of the skeleton ? 



2. What good purpose in having so many bones in the 

 skeleton ? 



3. Why is the axial skeleton made up of so many bones ? 



4. Why is the spinal column curved rather than straight ? 



d. Nervous System 



Materials. Demonstration specimens of nervous system of 

 a frog. 



Observations. 1. Find the brain of the frog. Note that in 

 front of the brain are two olfactory lobes leading to the nos- 

 trils. Just back of these find enlargements called cerebral 

 hemispheres; just back of these are the optic (sight) lobes or 

 midbrain, followed by a small cerebellum, which in turn is 

 followed by a long portion, the medulla oblongata, which 

 joins imperceptibly with the long dorsal nerve or spinal cord. 

 How far backwards does the spinal cord extend ? 



2. Note the many pairs of nerves given off from the brain 

 and spinal cord. Note. These nerves branch and rebranch 

 into very minute fibers some of which end in the muscles, 

 and are therefore called motor (motion) nerves. Still others 

 pass from the surface of the body inwards. They receive im- 

 pressions as of touch, light, heat, sound, etc., and are called 

 sensory nerves. 



3. Compare with the diagram of the nervous system of man. 

 Conclusion. If a sensory ending is affected by any external 



stimulus as noted above, where must the message be carried 

 before the muscles may be influenced ? 



