Question: what is the dense bone on the outside surfaces of a skeletal element called
[{'answer': 'cortical bone', 'provenance': [{'wikipedia_id': '4099', 'title': 'Bone', 'start_paragraph_id': 2, 'start_character': 689, 'end_paragraph_id': 2, 'end_character': 702, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '4099', 'title': 'Bone', 'start_paragraph_id': 10, 'start_character': 163, 'end_paragraph_id': 10, 'end_character': 1048, 'bleu_score': 0.790786967854311, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 1450091195662513034}, 'section': 'Section::::Structure.:Cortical bone.\n'}]}]