[R-sig-Geo] Getting polygons from list of lines

[r]

Hello,

I have got a list of lines given by a line number, the x and y coordinates of the start-point and 
of the end-point, like this:

LineNumber    X1     Y1     X2     Y2
1             64     169    108    162
2             108    162    141    179
3             108    162    119    133
4             141    179    188    179
5             188    179    168    134
6             188    179    233    152
7             233    152    229    117
8             229    117    168    134
9             168    134    119    133
10            119    133    37     132
11            37     132    64     169
12            83     93     37     132
13            83     93     139    96
14            139    96     119    133
15            139    96     197    85
16            197    85     229    117

These lines form a couple of simple polygons. Now I would like to have a list with the polygons 
delimited by these lines (for plotting and export into a external text file). Does anyone know a 
way how to do such a line-to-polygon conversion with R? Is there somewhere a package with 
such a function?

I did some search especially within the spatial packages, but I didn't find something.

Cheers,
Christian