A much cleaner, safer answer to this problem (you really shouldn't hard code Strings):
public void openInGallery(String imageId) {
Uri uri = MediaStore.Images.Media.EXTERNAL_CONTENT_URI.buildUpon().appendPath(imageId).build();
Intent intent = new Intent(Intent.ACTION_VIEW, uri);
startActivity(intent);
}
All you have to do is append the image id to the end of the path for the EXTERNAL_CONTENT_URI. Then launch an Intent with the View action, and the Uri.
The image id comes from querying the content resolver.