174 OSSEOUS SYSTEM. 



#. They prevent dislocations, and preserve the sym- 

 metry of the limb to which they are attached. 



Q. What general features are conspicuous in the bodies 

 of the long bdnes? 



t#. The ridges for the implanting of aponeuroses; and 

 the twist in most of these bones. 



Q. At what period is the medullary canal formed ? 



ft. At the period of ossification; it does not exist at the 

 earliest foetal periods. It is not found while the bone is 

 cartilaginous. 



Q. How is this canal formed? 



Jl. By the absorption of the gelatine in the centre, no 

 more of which is exhaled. Observe the different processes 

 which take place at the same time in the exterior and in- 

 terior of the bone; for, while the absorbents remove the 

 gelatine and thus form the medullary canal, and the exha- 

 lents cease to deposite gelatine, the exhalents on the ex- 

 ternal surface of the bone are placing a wall of phosphate 

 of lime to give the bone firmness and smoothness. 



Q. In what bones is the medullary canal found? 



*ft. In the humerus, in the radius, in the ulna, in the 

 femur, in the tibia, in the fibula, and in the clavicle. 



Q. What is the form of the canal ? 



/#. It is cylindrical and straight. 



Q. What are the uses of the medullary canal? 



t#. It gives lodgement and protection to the medullary 

 organ, and renders the bone stronger; for a hollow cylin- 

 der will be less apt to break or bend than a full one. 



Q. What would be the inconveniences of a solid cylin- 

 der for the shaft of a bone? "* 



#. They would impede the motion of the limbs, it 





