▁gives ▁them ▁their ▁bul ging ▁fore head , ▁and ▁they ▁have ▁a ▁large ▁sin us ▁that ▁is ▁closed ▁off ▁from ▁the ▁nas al ▁cav ity . ▁In ▁black - sp otted ▁c usc uses , ▁the ▁bas i oc cip ital ▁and ▁al is phen oid ▁b ones ▁in ▁the ▁sk ull ▁create ▁a ▁well - develop ed ▁structure ▁earlier ▁than ▁in ▁other ▁Ph al anger idae . ▁Their ▁eyes ▁are ▁character ized ▁by ▁large , ▁vert ically ▁split ▁pup ils ▁that ▁are ▁useful ▁for ▁their ▁no ct urn al ▁l ifest yle . ▁There ▁is ▁fur ▁l ining ▁the ▁inner ▁ears , ▁which ▁are ▁almost ▁invisible . ▁Black - sp otted ▁c usc uses ▁can ▁be ▁distinguished ▁from ▁other ▁c usc uses ▁by ▁their ▁teeth . ▁They ▁have ▁low ▁crow ns ▁and ▁small ▁prem ol ars ▁that ▁lie ▁anterior ▁to ▁the ▁primary ▁prem olar ▁in ▁the ▁upper ▁j aw . ▁In ▁addition , ▁they ▁have ▁a ▁prominent ▁proto con e ▁on ▁their ▁first , ▁upper ▁mol ars . ▁ ▁They ▁have ▁arch ed ▁front ▁cla ws ▁that ▁are ▁pointed ▁ac utely ▁for ▁the ▁purpose ▁of ▁clim bing . ▁The ▁first ▁two ▁digits ▁on ▁these ▁forec la ws ▁are ▁oppos able ▁to ▁the ▁other ▁three ▁digits . ▁The ▁to es ▁of ▁the ▁h ind ▁feet ▁have ▁adapted ▁to ▁grasp ▁objects ▁and ▁branches ; ▁the ▁oppos able ▁big ▁toe ▁has ▁no ▁cla ws , ▁while ▁the ▁smaller ▁second ▁and ▁third ▁to es ▁are ▁f used ▁together . ▁ ▁Black - sp otted ▁c usc