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Ultrastructural observations on the tendon sheath of the rat tail.

The ultrastructure of the tendon sheath of the rat tail was examined with scanning and transmission electron microscopes. The tendon sheath was divided into three layers: the visceral, parietal and fibrous layers. By scanning electron microscopy, the longitudinal shallow ridges approximately 7 microns wide were seen on the surface of the visceral layer. On the other hand, the spiral ridges approximately 20 microns wide running at an angle of 35 degrees to the longitudinal axis were exposed clearly on the inner surface of the parietal layer. Blood capillary networks were also observed on the surface of the parietal layer, especially in the specimens treated with HCl. The fibrous layer of the tendon sheath was characterized by a large number of collagen fibers in a woven arrangement. The inner surface of the fibrous layer showed spiral ridges similar to that of the parietal layer, suggesting that the ridges of parietal and fibrous layers were concerned with the arrangement of collagen fibers in the innermost region of the fibrous layer.