The structure and function of the ureter in the dog.

THE structure of the ureter was investigated by the examination of sections taken from the ureters of 14 dogs. Simultaneous recordings of peristalsis under conditions of varying urine flow were made from the middle and lower segments of the ureters of 10 dogs under anaesthesia by means of a method that allowed free urine flow.The ureter was found to possess three layers of muscle in its wall, an inner and outer longitudinal layer and a middle layer of fibres whose orientation varied from circular to oblique. On the basis of the arrangement of these three layers the ureter can be divided in its length into three segments. The middle segment has the most completely circular fibres in its middle layer and the junction between it and the upper and lower segments are marked by a change in the orientation of the middle layer fibres from circular in the middle segment to oblique in the upper and lower.Evidence is provided by pressure measurements that these changes provided the basis for sphincteric mechanisms at high rates of urine flow.