352 MINUTE STRUCTURE OF BONE. 



tebra will then be seen to be, essentially, a ring, or padlock, 

 consisting of the body and neural ring or arch. 



Examine the cavity of the skull. If the class has not a 

 skull which has been sawed across, look into the skull cavity 

 through the hole where the spinal cord joined the brain. 



Observe the conical shape of the thorax. In the entire 

 body the bones and muscles about the shoulders usually make 

 a reversed cone of the upper part of the trunk. 



Observe that the ribs are connected with the breastbone by 

 cartilages. 



The upper limbs are articulated with the body only where 

 the inner ends of the collar bones join the breastbone. 



Rest the forearm on the table with the palm up ; keeping 

 the elbow fixed, turn the hand over. Turning the palm up is 

 called Supination ; turning it down is Pronation. Perform 

 this experiment with the articulated skeleton. 



Examine the skeleton of a cat or rabbit for the sake of 

 comparison. Note especially the skull and spinal column, so 

 that you will know better what to do when dissecting the 

 brain and spinal cord in one of these animals. 



The bones make about one-sixth of the weight of the 

 living body. When dried they may lose half of their 

 weight. 



Microscopic Structure of Bone. 1. Hold a mounted 

 cross section of bone up to the light, and examine it with a 

 hand lens. The solid part of the bone will be seen to be 

 pierced by many small holes (or if the holes are filled they 

 will appear as. black spots). These are the cross sections of 

 the Haversian Canals, through which run the blood tubes, 

 mainly lengthwise through the bone. 



2. Examine the section under the microscope, using a half- 

 inch objective. 



The bony matter will now be seen to be arranged in 



