访问R包中的子目录

I have a data folder in an R package. With in the the data directory I have a sub directory data/JE. I want to access this directory and apply list.file function and then using the list I want to read each file. I can setwd() when not running the package. But while the package is running I don't know how to access the directory.I have a data folder in an R package. With in t