After detailed study of the anorectal morphology on three Wistar and three BDIX rats, we designed a simple procedure, as follows (Figure 1 ).
Firstly, the animal was placed over a heating blanket, in a supine position. Perineal antisepsis was performed. The anal canal was emptied and a probe (Abbocath® 14G or similar) was inserted through it.
An arciform 10 mm to 15 mm anterior perianal incision (3 mm from verge) was performed. A 6/0 stitch at the inferior border to the tail was knotted. Adipose tissue was dissected sideways (with scissors or gauze) to expose approximately 20 mm of anorectal conduit until visualization of a thin darker line (external sphincter) or up to the anal verge.
Then, the muscular layer was held with clamps and a small incision was made until herniation of the submucosa or the probe was visualized by transparency. Submucosal dissection was continued longitudinally and the muscular layer was sectioned in a longitudinal fashion up to the anal verge and near the stitch caudally and proximally until completing 10 mm. If a mucosal perforation occurred, an interrupted suture was performed, leaving knots on the parietal side.
Firstly, the animal was placed over a heating blanket, in a supine position. Perineal antisepsis was performed. The anal canal was emptied and a probe (Abbocath® 14G or similar) was inserted through it.
An arciform 10 mm to 15 mm anterior perianal incision (3 mm from verge) was performed. A 6/0 stitch at the inferior border to the tail was knotted. Adipose tissue was dissected sideways (with scissors or gauze) to expose approximately 20 mm of anorectal conduit until visualization of a thin darker line (external sphincter) or up to the anal verge.
Then, the muscular layer was held with clamps and a small incision was made until herniation of the submucosa or the probe was visualized by transparency. Submucosal dissection was continued longitudinally and the muscular layer was sectioned in a longitudinal fashion up to the anal verge and near the stitch caudally and proximally until completing 10 mm. If a mucosal perforation occurred, an interrupted suture was performed, leaving knots on the parietal side.
