The three-dimensional structure of the musculature and the nerve elements in the rabbit ureter.

The three-dimensional arrangement of muscle fibres and nerve elements in the rabbit ureter was examined by scanning electron microscopy after removal of fibrous elements by the HCl-trypsin digestion method. The ureteral muscle coat consisted of an interlacing network of muscle bundles made up of varying numbers of smooth muscle cells. On the outer surface of the muscle coat the muscle bundles predominantly extended transversely but some of them continued longitudinally. Some small bundles diverged from the main bundle and joined up with neighbouring or distant bundles. In most regions of the muscle coat irregular membranous or bifurcating cells were sometimes observed. On the longitudinally cut surface of the ureter, polygonal profiles of the cross-sectioned cells and elongated profiles of the longitudinally-sectioned cells were observed in the same bundle. The variety of these cut profiles suggested the differing directions of the muscle Some small interconnecting bundles extended across the inter-bundle spaces. Neighbouring muscle cells were connected laterally by short processes and were joined by gap junctions and desmosomal junctions; these were seen by transmission electron microscopy in thin sections and by freeze-fracture replicas. Thread-like nerve fibres were seen to be lying individually or in a fasciculus. Their terminals were characterised by varicose swellings. Streaks indicting mesaxonal extensions were exhibited on the Schwann cells enclosing nerve fibres.