{HEAD ~ Each} of the sides has {TAIL ~ an empty space frame} by outer edges of the housing side 
has
{ HEAD ~ Each } of the sides has { TAIL ~ an empty space frame } by outer edges of the housing side
HEAD HEAD HEAD HEAD HEAD OTH OTH OTH REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH