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Penis.

As the vas deferens nears the distal end of the penis, its wall becomes thickened by a dense layer of circular muscle. This layer merges into the penis sheath, and becomes separated from the penis proper by a fluid-filled space. No longitudinal muscle fibres are present in the sheath. Inside the sheath, the heavily convoluted and folded penis is lined by ridged columnar epithelium resting on connective tissue and surrounded by an inner circular and an outer longitudinal muscle layer. Thick mucus lines the lumen of the penis. As the penis nears its junction with the uterus and vagina, the folding and ridging of the epithelium becomes more prominent, and the muscle layers thicker. The penis sheath merges with the penis at the junction with the uterus and vagina (Fig. 14).