» The Rectum and Anus

The shortness of its mesentery is the only additional point that need be made concerning the rectum. Congenital absence of the anus (atresia ani) once was of frequent occurrence; perhaps surprisingly, it may allow afflicted piglets to survive for 3 or 4 weeks without treatment.

Prolapse of the rectum, encountered in somewhat older pigs, requires more sophisticated surgery, especially if the everted bowel has been mutilated by pen mates, as so often happens. The muscles of the anus are more or less as in other species (see Figs. 3.47 and 3.48): bundling together of the longitudinal muscle of the rectum creates the rectococcygeus, and thickening of the circular muscle creates the internal anal sphincter. There is a striated external sphincter. The levator ani runs between the sacrosciatic ligament and the lateral aspect of the anal canal, and the two retractor penis (or clitoridis) muscles form a sling below the rectum before continuing to the penis (or clitoris).