Question: which layer of the meninges is connected to the brain
[{'answer': 'pia mater', 'provenance': [{'wikipedia_id': '398932', 'title': 'Meninges', 'start_paragraph_id': 1, 'start_character': 214, 'end_paragraph_id': 1, 'end_character': 223, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'answer': 'The pia mater', 'provenance': [{'wikipedia_id': '398932', 'title': 'Meninges', 'start_paragraph_id': 15, 'start_character': 0, 'end_paragraph_id': 15, 'end_character': 13, 'bleu_score': 1.0, 'section': 'Section::::Structure.:Pia mater.\n'}]}, {'provenance': [{'wikipedia_id': '398932', 'title': 'Meninges', 'start_paragraph_id': 15, 'start_character': 0, 'end_paragraph_id': 15, 'end_character': 453, 'bleu_score': 0.9245712963830611, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 17874806481394034375}, 'section': 'Section::::Structure.:Pia mater.\n'}]}, {'provenance': [{'wikipedia_id': '398932', 'title': 'Meninges', 'start_paragraph_id': 0, 'start_character': 0, 'end_paragraph_id': 0, 'end_character': 0, 'bleu_score': 1.0, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 17874806481394034375}, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '21009963', 'title': 'Meningitis', 'section': 'Section::::Mechanism.\n', 'start_paragraph_id': 34, 'end_paragraph_id': 34, 'meta': {'evidence_span': ['space. Rarely, migraine may cause meningitis, but this diagnosis is usually only made when other causes have been eliminated. The meninges comprise three membranes that, together with the cerebrospinal fluid, enclose and protect the brain and spinal cord (the central nervous system). The pia mater is a very delicate impermeable membrane that firmly adheres to the surface of the brain, following all the minor contours. The arachnoid mater (so named because of its spider-web-like appearance) is a loosely fitting sac on top of the pia mater. The subarachnoid space separates the arachnoid and pia mater membranes and is filled with cerebrospinal fluid. The outermost membrane, the dura mater, is a thick durable membrane, which is attached to both the arachnoid membrane and the skull.', 'The pia mater is a very delicate impermeable membrane that firmly adheres to the surface of the brain, following all the minor contours', 'The pia mater is a very delicate impermeable membrane that firmly adheres to the surface of the brain, following all the minor contours. The arachnoid mater (so named']}}]}, {'provenance': [{'wikipedia_id': '398932', 'title': 'Meninges', 'section': 'Section::::Structure.:Arachnoid mater.\n', 'start_paragraph_id': 12, 'end_paragraph_id': 12, 'meta': {'evidence_span': ['system. This thin, transparent membrane is composed of fibrous tissue and, like the pia mater, is covered by flat cells also thought to be impermeable to fluid. The shape of the arachnoid does not follow the convolutions of the surface of the brain and so looks like a loosely fitting sac. In particular, in the region of the brain a large number of fine filaments called arachnoid trabeculae pass from the arachnoid through the subarachnoid space to blend with the tissue of the pia mater. The arachnoid is composed of an outermost portion (arachnoid barrier cell layer) with tightly packed cells and no extracellular collagen; that is why it is considered to represent an effective morphological and physiological meningeal barrier between the cerebrospinal fluid and subarachnoid space and the blood circulation in the dura.', 'This thin, transparent membrane is composed of fibrous tissue and, like the pia mater, is covered by flat cells also thought to be impermeable to fluid.', 'ystem. This thin, transparent membrane is composed of fibrous tissue and, like the pia mater,']}}]}, {'provenance': [{'wikipedia_id': '398932', 'title': 'Meninges', 'section': 'Section::::Structure.:Pia mater.\n', 'start_paragraph_id': 15, 'end_paragraph_id': 15, 'meta': {'evidence_span': ["The pia mater () is a very delicate membrane. It is the meningeal envelope that firmly adheres to the surface of the brain and spinal cord, following all of the brain's contours (the gyri and sulci). It is a very thin membrane composed of fibrous tissue covered on its outer surface by a sheet of flat cells thought to be impermeable to fluid. The pia mater is pierced by blood vessels to the brain and spinal cord, and its capillaries nourish the brain.", "The pia mater () is a very delicate membrane. It is the meningeal envelope that firmly adheres to the surface of the brain and spinal cord, following all of the brain's contours (the gyri and sulci)", 'he pia mater is pierced by blood vessels to the brain and spinal cord, and its capillaries nourish the brain.']}}]}]