Structures of the iris

Structures of the iris. The a indicates the anterior border layer that terminates at the pigmentary ruff of the pupillary border (b). The c indicates the iris sphincter muscle, which is oriented circumferentially within the stroma and located deep to the anterior border layer; d indicates vessels that traverse the stroma and sphincter muscle; f indicates the iris dilator muscle, which is oriented radially and located deep to the stroma. The dilator terminates at the mid-sphincter position (arrow), at which point cuboidal epithelial cells (g) continue to the pupillary margin to form the anterior epithelial layer; j indicates the tall columnar cells that make up the posterior epithelial layer. (Hogan MJ, Alvarado JA, Weddell JE [eds.]: Histology of the Human Eye. An Atlas and Textbook, p 231. Philadelphia: WB Saunders, 1971, with permission.)