Spatial topography of the excurrent duct system in the bovine testis.

The rete testis of the bull is situated within an axial mediastinum and consists of approximately 30 longitudinally arranged, anastomosing rete channels. At the cranial testicular pole all rete channels empty into a common space, the area confluens retis, which is subdivided by small septa and narrow chordae retis. The area confluens always contains numerous spermatozoa and is connected with the bulbous initial portions of the efferent ductules by short, often tortuous rete tubules. Since the connection between rete and efferent ductules is situated within the tunica albuginea, the bovine excurrent duct system is not provided with an extratesticular rete as in many other mammals. Straight testicular tubules merge from all directions to connect with superficial rete channels, but the inlets are not evenly distributed. In the periphery each straight tubule begins with a cup-like structure followed by a narrow stalk region and a heavily folded portion opening either immediately into a rete channel or into a tube-like lateral rete extension. In close contiguity to the rete testis lie extremely coiled arterial portions connecting the centripetal and the centrifugal branches of the testicular artery. Since intrinsic musculature is scarcely developed in the mediastinum, and transport of rete content relies primarily on massage due to external pressure changes, the pulsatile blood flow through these coiled arteries may influence conveyance processes within the rete testis. An intimate spatial association between area confluens retis and adjacent large, thin-walled lymph vessels may facilitate a transfer of androgens into the fluid of the rete testis.