鼠标的中键怎么启用？

midx

xorg.conf关于鼠标的一段：

1. Section "InputDevice"
   
2. 
   
3. # Identifier and driver
   
4. 
   
5.     Identifier        "Mouse1"
   
6.     Driver "mouse"
   
7.     Option "Protocol"   "ImPS/2"
   
8.     Option "ZAxisMapping"   "4 5"
   
9.     Option "Device"     "/dev/psaux"
   
10. 
    
11. # When using XQUEUE, comment out the above two lines, and uncomment
    
12. # the following line.
    
13. 
    
14. #    Option "Protocol"   "Xqueue"
    
15. 
    
16. # Baudrate and SampleRate are only for some Logitech mice. In
    
17. # almost every case these lines should be omitted.
    
18. 
    
19. #    Option "BaudRate"   "9600"
    
20. #    Option "SampleRate" "150"
    
21. 
    
22. # Emulate3Buttons is an option for 2-button Microsoft mice
    
23. # Emulate3Timeout is the timeout in milliseconds (default is 50ms)
    
24. 
    
25. #    Option "Emulate3Buttons"
    
26. #    Option "Emulate3Timeout"    "50"
    
27. 
    
28. # ChordMiddle is an option for some 3-button Logitech mice
    
29. 
    
30. #    Option "ChordMiddle"
    
31. 
    
32. EndSection

复制代码

滚轮能正常使用，只是滚轮按下作为中键使用的功能无效。
哪里不对呢？