The components of the levator ani are therefore named the pubococcygeus, ileococcygeus, and ischiococcygeus. The pubococcygeus is further subdivided to include the puborectalis. Between the urogenital viscera and the anal canal lies the perineal body. The perineal body consists of the superficial and deep transverse perinei muscles and the ventral extension of the external sphincter muscle to a tendinous intersection with the bulbocavernosus muscle. The fourth sacral nerve innervates the levator ani muscles.
Controversy continues regarding the innervation and origin of the puborectalis muscle.
Cadaver studies differ from in vivo stimulation studies as to whether the puborectalis muscle receives innervation only from the sacral nerve or also from the pudendal nerve. Comparative anatomy and histological studies of fiber typing also support the inclusion of the puborectalis muscle with the sphincter complex and not as a pelvic floor muscle. In addition, EMG studies of the external anal sphincter and puborectalis muscle indicate that the muscles function together with cough and strain. The anal canal is approximately 4 cm long and extends from the anal verge to the top of the external anal sphincter complex or ring. This is a clinical and surgical description that corresponds to the digital exam and findings seen on ultrasound but not to the histological changes along the canal.