18. What is the name of the structure seen to the right?
Label the three parts composing this structure.
How are the three parts held together?
![18 What is the name of the structure seen to the right Label the three parts composing this structure How are the three parts held together class=](https://us-static.z-dn.net/files/de4/0dfe9a8878d174b32372e3acdf8b0473.png)