arachnoid

& s. [In Fr. arachnoide. From Gr. ἀράχνης (arachnēs) and ἀράχνη (arachne) = a spider, and εἶδος ( eidos ) = form.] A. As adjective: L Anat .: Of the form or aspect of a spider's web. Specially 1. Pertaining to the membrane of the brain called the Arachnoid. (Todd & Bowman: Physiol. Anat., vol. ii., p. 253.) 2. Pertaining to the tunic of the crystalline humour of the eye. 3. Pertaining to one of the coverings of the spinal marrow. IMG:content-0687.jpg:[blocks in formation] B. As substantive (Anatomy): 1. The serous membrane of the cranio-spinal cavity. It adheres to the dura mater by its parietal layer, and with the intervention of the pia mater to the brain and spinal cord by its visceral layer. (Todd & Bowman: Physiol. Anat ., vol. ii., p. 253.) 2. The capsule of the crystalline lens, which is a continuation of the hyaloid membrane. [A RACH NO IDES.] arachnoid cavity. The space between the two layers of the arachnoid membrane. (Todd & Bowman: Physiol. Anat . , ii. 253.) arachnoid membrane. [ARACHNOID (Β. 1).]