The middle muscularis of the ureter consists of an inner layer and an outer circular layer.

The middle muscularis of the ureter is made up of two layers of smooth muscle tissue. The inner layer is arranged in a longitudinal fashion, meaning the muscle fibers run lengthwise down the ureter. This layer helps propel urine down the ureter and into the bladder.

The outer layer, on the other hand, is arranged in a circular fashion. This means the muscle fibers wrap around the ureter. This layer helps keep the shape of the ureter and prevent it from collapsing. It also assists in the propulsion of urine.

Together, these two layers of muscle in the middle muscularis allow the ureter to actively push urine down into the bladder, rather than just letting it passively flow down. This is important because it allows the body to more effectively clear waste from the kidneys.