Anal Canal

Although the anal canal has been variously defined, the definition that has practical clinical forensic value is that of the anatomical anal canal, which extends from the anus to the dentate line. The dentate line refers to the line formed either by the bases of the anal columns (most distinct in children) or, when these are not apparent, by the lowest visible anal sinuses (175). The average length of the anatomical anal canal in adults (age range 18-90 years) is only 2.1 cm, with a range of 1.4-3.8 cm in males and 1.0-3.2 cm in females (176). Between the epithelial zones of the anal canal and the rectum is the anal transitional zone, which is usually located in the region of the anal columns and is purple (177).

The anal canal, as previously defined, is lined by nonkeratinized squamous epithelium and is salmon pink in the living (174). It is sensitive to touch, pain, heat, and cold to just above the dentate line (175). The anus and lumen of the anal canal usually appear as an asymmetric Y-shaped slit when viewed via a proctoscope (anoscope). The folds of mucosa and subcutaneous tissue (containing small convulated blood vessels surrounded by connective tissue) between the indentations of the Y are referred to as the anal cushions. Although this appearance is usually obscured externally by the folds of skin on the perianal area, it may become apparent if the patient is anesthetized or as the anus dilates.

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