The epithelium of the common ejaculatory chamber and the distal 0.5 cm of the ducts of the seminal vesicles and of the vasa deferentia, as well as the uterus masculinus throughout all its length, except for the bifid tips, is stratified. Since this epithelium resembles that lining the urogenital sinus of the fetus and is derived from it, we have termed it a "sinus epithelium." It is abruptly continuous with the transitional epithelium of the proximal urethra at the lips of the common midline orifice of the ejaculatory chamber. The "sinus epithelium," as well as the transitional epithelium of the proximal urethra, shows thickening, increased stratification, and many areas of superficial mucification and mucous crypt formation in the neonatal animal. The sinus epithelium is atrophic in the sexually immature animal, and again is hyperplastic and mucified in the mature animal.

The prostate and coagulating glands consist of 6-7 major lobes loosely bound together by connective tissue, and the ducts opening into the urethra are equal in number to that of the major lobes. Each lobe may be further subdivided by dissection into many lobules, cylindrical in form, these being wider and more blunt in the coagulating gland. The even distribution of the lobes around the common ejaculatory chamber and urethra does not justify their subdivision into discrete dorsal and ventral or lateral entities as conventionally described.