The pelvis of the kidney and its calices
The pelvis of the kidney and its calices are lined with transitional epithelium. It consists of only three or four layers of epithelial cells of different shapes. The most superficial layer is composed of rather large flattened cells, having ridges upon their lower surfaces, which fill the spaces between the tops of the next layer. This is made up of pear-shaped or caudate cells, the hemi- spherical tops of which fit into the cavities between the ridges on the layer above, while their slender processes penetrate between the oval or round cells that make up the deepest layers of the epithelial covering.
Beneath the epithelium is a coat of fibrous tissue, denser near the epithelium and more areolar in its deeper portions. Here it is interlaced with smooth muscular fibers, outside of which is the external coat of fibrous tissue.
The ureters closely resemble in structure the pelvis of the kidney ; but the muscular fibers have a somewhat more definite arrangement, being disposed in an inner imperfect coat of longitudinal and an external layer of circular fibers, outside of which a few supplementary longitudinal fibers are, here and there, added.