[R] Variable descriptions of a built-in dataset

[Jun Ding]

Hi, everyone, 
Is there a way to get the detailed variable
descriptions of a built-in dataset?

By using 
 attributes(Boston)
I can get the names of each variables of a builtin
dataset 'Boston'(in package "MASS"), but I don't know
what each variable means. Can some body tell me how I
can get more detailed information about each variable?
Thank you!

Jun