334 APPENDIX. - 



on the vertebrae, or back-bone. Cristce, or crests, are 

 long, sharp elevations, as the crista galli of the ethmoid, 

 one of the bones of the head. Trochanter, whicH means 

 to run or roll, is applied to two eminences situated on 

 the upper part of the thigh bone. They are so named 

 because to these parts are attached the large muscles by 

 the action of which the limb is turned or moved. 



Depressions. Some of the depressions in the bones 

 are of considerable depth, while others are quite superfi- 

 cial. That which receives the head of the thigh bone is 

 the deepest, and is called the cotyloid cavity. Those in 

 which the teeth are fixed are called alveoli, or sockets. 

 Those which are more shallow are called glenoid, as the 

 cavity in the scapula, or shoulder-blade, which receives 

 the head of the humerus. 



PERIOSTEUM. 



Periosteum signifies around the bone, and is applied 

 to the membrane which surrounds all the bones in every 

 part of the skeleton, except when they are tipped with 

 cartilage, and the teeth, which are protected by enamel. 



In infancy this covering is but slightly united to the 

 bones, and is removed from them with facility ; but in 

 the adult it adheres firmly, and in old age can not be de- 

 tached. 



In the healthy state, the periosteum, like the bones, is 

 without sensibility ; but when diseased, it becomes ex- 

 ceedingly painful. This is a proof that it is furnished 

 with nerves, though they are too minute to be demonstra- 

 ted to the sight. 



It is this membrane which gives vitality to the bones, 

 for when separated from them, their surfaces perish, and 

 exfoliate. To it are also attached the tendons, ligaments, 

 and muscles. 



What are the crista ? What are the trochanters ? What is the cotyloid 

 cavity ? What are glenoid cavities ? What is the meaning of periosteum ? 

 What the uses of this membrane ? 



