▁is ▁the ▁linea ▁sem il un aris . ▁ ▁In ▁the ▁ab dom ens ▁of ▁people ▁with ▁low ▁body ▁fat , ▁these ▁mus cle ▁bel lies ▁can ▁be ▁viewed ▁extern ally ▁and ▁are ▁commonly ▁referred ▁to ▁as ▁" four ", ▁" six ", ▁" e ight ", ▁or ▁" ten ▁pack s ", ▁depending ▁on ▁how ▁many ▁are ▁visible ; ▁although , ▁six ▁is ▁the ▁most ▁common . ▁ ▁Str ucture ▁The ▁rect us ▁ab domin is ▁is ▁a ▁long ▁flat ▁mus cle , ▁which ▁extends ▁along ▁the ▁whole ▁length ▁of ▁the ▁front ▁of ▁the ▁ab d omen , ▁and ▁is ▁separated ▁from ▁its ▁fellow ▁of ▁the ▁opposite ▁side ▁by ▁the ▁linea ▁al ba . ▁T end in ous ▁inter sections ▁( in cription es ▁tend inae ) ▁further ▁sub div ide ▁each ▁rect us ▁ab domin is ▁mus cle ▁into ▁a ▁series ▁of ▁smaller ▁false ▁mus cle ▁bel lies . ▁T ens ing ▁of ▁the ▁rect us ▁ab domin is ▁causes ▁the ▁mus cle ▁to ▁expand ▁between ▁each ▁tend in ous ▁intersection , ▁resulting ▁in ▁the ▁characteristic ▁six ▁or ▁eight ▁pack ▁observed ▁in ▁individuals ▁with ▁low ▁body ▁fat . ▁ ▁The ▁upper ▁portion , ▁attached ▁princip ally ▁to ▁the ▁cart il age ▁of ▁the ▁fifth ▁rib , ▁usually ▁has ▁some ▁fib ers ▁of ▁insert ion ▁into ▁the ▁anterior ▁extrem ity ▁of ▁the ▁rib ▁itself . ▁ ▁Size ▁ ▁It ▁is ▁typically ▁around ▁ 1 0   mm ▁thick ▁( comp ared ▁to ▁ 2 0   mm ▁thick ▁super f icial ▁fat