THE JOINTS. 19 



B. A Ball and Socket Joint. 



Material. A fresh hip-joint of an ox or sheep with the mem- 

 brane and muscles still attached. If the butcher saws it in halves 

 longitudinally, the different parts may be clearly seen. 



Study carefully a large, fresh ball and socket joint, such 

 as the hip-joint of a sheep. 

 Identify : 



a. The cavity, or acetabulum. What is its shape and 

 use? 



b. The ball, or head of the long bone. What is its 

 shape and use ? 



c. The cartilage. 



1. How far does it extend? 



2. Feel of it. 



3. Cut it. 



4. What are its properties and uses ? 



d. The ligaments bind the bones together. Find the use 

 and the properties of each. 



1. The capsular ligament is a loose bag extending 



all around the joint. 



2. The round ligament passes from the acetabulum 



to the head of the long bone. How does the 

 attachment of these ligaments allow motion at 

 the joint? 



e. The tendons attach the muscles to the bones. How 

 do they differ in appearance from the ligaments ? 



/. The synovial membrane is a thin layer of cells extend- 

 ing over the ligaments and cartilage. It is too thin to be 

 distinguished with the naked eye. 



