When open, a keyboard having {HEAD ~ keys} that are apportioned between {TAIL ~ the housing} and the base is accessible 
are apportioned between
When open , a keyboard having { HEAD ~ keys } that are apportioned between { TAIL ~ the housing } and the base is accessible
OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD OTH REL REL REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH