The Penis and Prepuce
The penis, broadly similar to that of the bull, is relatively thin, exhibits a prescrotal sigmoid flexure, and is about 60 cm long (when flaccid) (Fig. 35.6/10). A thick tunica albuginea encloses the corpus cavernosum (Fig.
35.9/1). The corpus spongiosum lies first on the ventral surface of the corpus cavernosum, but more distally it is recessed in a deep groove that brings it to a central position (Fig. 35.9B/6). Apart from the sigmoid flexure, the shaft is twisted on its longitudinal axis a full turn counterclockwise (when viewed from behind). The direction of the twist is the same as that of the spiral of the apex (Fig. 35.9C).The relatively long prepuce houses the free part of the penis in its narrow caudal half. The wider cranial half communicates with a dorsal diverticulum, a pouch containing an evil-smelling fluid consisting of cell debris soaked in urine (Fig. 35.6/9 and 11). The diverticulum is covered by the cranial preputial muscle, which empties it before copulation (Fig. 35.10A/1). The fluid contains a pheromone that encourages the sow to assume the immobile mating stance. If the contents of the diverticulum collect excessively, the appearance may mimic umbilical hernia. An infected diverticulum may be opened and drained through a dorsolateral incision that inevitably includes the muscle. The diverticulum is sometimes removed in boars used for artificial insemination so that contamination of the semen is reduced. Although the tip of the penis occasionally becomes entrapped in the diverticulum, it is readily freed.