These oligodendrocytes can then wrap damaged axons with new myelin sheaths. Demyelinating plaques attack the myelin sheaths on neurons. During infancy, myelination progresses rapidly, with increasing numbers of axons acquiring myelin sheaths. Therefore, unlike Schwann cells, oligodendrocytes fail to clean up the myelin sheaths and their debris. This discovery later led Ranvier to careful histological examination of myelin sheaths and Schwann cells. The leaves of horsetails are arranged in whorls fused into nodal sheaths. Research to repair damaged myelin sheaths is ongoing. In the distal leaves, the blades are narrower than the open, spread leaf sheaths. Nylon has been used for meat wrappings and sausage sheaths. Less commonly ectasia of the sacral nerve root sheaths may occur. It consists of the single species with persistent fascicle sheaths. During the Khiamian, bone was used for needles, awls and axe sheaths. Cable harnesses can be built using aircraft steel cables, ball hinges, and self-lubricating cable sheaths. Gloves usually have separate sheaths or openings for each finger and the thumb. The sheaths of the tusks were parallel and spaced closely.