Short cords may be observed. Although the internal separation of the cloaca by the urorectal septum is not yet complete, a transverse bar of mesenchyme apparently spans the urethral groove forming an anal pit at the basal end of the tubercle. The mammary crest may be identified. The genital tubercle has formed a compressed ,conical protuberance and the future glans and shaft regions of the phallus may be determined. The urethral folds merge distally into the glans region of the tubercle and basally with the anal tubercles.
Nipples appear on the mammary crest.
The gonads begin to differentiate. They become a distinct swelling extending to the rostral pole of the mesonephros and primary sex cords develop in both the cortical and medullary regions of the gonad. Cells in the cortical region degenerate. This is based on studies of embryo s between 16 and 17mm long although some may belong to stage 19. The development of the gonads now reaches a phase of differentiation when they become histologically distinct in the male and female.