Henry Gray (18251861). Anatomy of the Human Body. 1918.
deeply between the Levator ani and Obturator internus into a space known as the ischiorectal fossa.
The Deep Fascia.The deep fascia forms the lining of the ischiorectal fossa; it comprises the anal fascia, and the portion of obturator fascia below the origin of Levator ani.
Ischiorectal Fossa (fossa ischiorectalis) (Fig. 405).The fossa is somewhat prismatic in shape, with its base directed to the surface of the perineum, and its apex at the line of meeting of the obturator and anal fasciæ. It is bounded medially by the Sphincter ani externus and the anal fascia; laterally, by the tuberosity of the ischium and the obturator fascia; anteriorly, by the fascia of Colles covering the Transversus perinæi superficialis, and by the inferior fascia of the urogenital diaphragm; posteriorly, by the Glutæus maximus and the sacrotuberous ligament. Crossing the space transversely are the inferior hemorrhoidal vessels and nerves; at the back part are the perineal and perforating cutaneous branches of the pudendal plexus; while from the forepart the posterior scrotal (or labial) vessels and nerves emerge. The internal pudendal vessels and pudendal nerve lie in Alcocks canal on the lateral wall. The fossa is filled with fatty tissue across which numerous fibrous bands extend from side to side.
FIG. 405 The perineum. The integument and superficial layer of superficial fascia reflected. (See enlarged image)
The Corrugator Cutis Ani.Around the anus is a thin stratum of involuntary muscular fiber, which radiates from the orifice. Medially the fibers fade off into the submucous tissue, while laterally they blend with the true skin. By its contraction it raises the skin into ridges around the margin of the anus.
The Sphincter ani externus (External sphincter ani) (Fig 405) is a flat plane of muscular fibers, elliptical in shape and intimately adherent to the integument surrounding the margin of the anus. It measures about 8 to 10 cm. in length, from its anterior to its posterior extremity, and is about 2.5 cm. broad opposite the anus. It consists of two strata, superficial and deep. The superficial, constituting