| cerebral part of arachnoid | That portion of the arachnoid which lies within the cranial cavity and surrounds the brain and the cranial portion of the subarachnoid space. In several sites it is relatively widely-separated from the pia mater, creating the cranial subarachnoid cisterns. Synonym: arachnoid mater cranialis, arachnoid mater encephali, cerebral part of arachnoid. (05 Mar 2000) |
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| pia-arachnoid | The two delicate layers of the meninges, the arachnoid mater and pia mater (vs. The tough pachymeninx or dura mater), considered together; by this concept, the arachnoid and pia are two parts of a single layer, much like the parietal and visceral layers of a serous membrane or bursa; although separated by the subarachnoid space they are connected via the arachnoid trabeculae and become continuous where the nerves and filum terminale exit the subarachnoid space (the cerebrospinal fluid-filled space bounded by the leptomeninges). See: arachnoid, pia mater. Synonym: meninx tenuis, pia-arachnoid, piarachnoid. Origin: Lepto-+ G. Meninx, pl. Meninges, membrane (05 Mar 2000) |
| spinal part of arachnoid | That portion of the arachnoid which lies within the vertebral canal and surrounds the spinal cord and the vertebral portion of the subarachnoid space. It extends from the foramen magnum above to the S-2 vertebral level. Since the spinal cord ends at the L-2 vertebral level, a wide separation occurs between the arachnoid and pia mater, the lumbar cistern, filled with cerebrospinal fluid in which the cauda equina is suspended. Synonym: arachnoidea mater spinalis, spinal part of arachnoid. (05 Mar 2000) |