"The late Dr. W. E. Horner, Professor of Anatomy in the University of Pennsylvania, used to describe an arrangement of pouches opening upward, in the mucous membrane of the rectum, by which the entanglement of seeds, bits of bone, etc., contained in the feces was favored. His account may be found in his 'Special Anatomy and Histology,' vol. ii, p. 46 (edition of 1851), where he quotes a paper on Fistula in Ano, by Ribes. He says, also, that Glisson and Ruysch had described them as valves, and that Winslow was acquainted with them. The latter author (Douglas's Transl., 1743, vol. ii, p. 149) says, 'They form little bags or semilunar lacunæ.' Another American writer, Bushe ('Malformations, Diseases, and Injuries of the Rectum and Anus,' 1837, p. 15), speaks of these pouches, and confirms Winslow's description. They are also mentioned in the treatises of Leidy and S. G. Morton. Hyrtl (Handb. der Topogr. Anatomie, 1871, bd. ii, p. 142) describes them quite fully, and speaks of their agency in the development of fistulæ. "Mr. W. T. Clegg, of Liverpool, says (Lancet, Feb. 5, 1881) that Mr. Bickersteth has for four years been describing these anal pouches, which 'are not mentioned in any of the books he has consulted.' "It is certainly strange that this arrangement, so clearly pointed out, should have been passed over in silence, not only by many anatomists, but by late writers on rectal surgery; yet it is undoubtedly a frequent cause of fistula. In Fig. 14 these pouches are shown, with a fistula, probably formed by a foreign body lodging in one of them. Over the fistula the mucous membrane has been removed, and a bougie has been passed through the canal."[41] [Illustration: Fig. 14—Section of the Rectum, showing the rectal pouches, and a fistula with a bougie passed through it, the mucous membrane dissected off. At _a_ is a small external pile, cut in half.—St. George's Hospital Museum, ser. ix, No. 42 (Holmes, Princ. and Pract. of Surgery, vol. ii, p. 643).] Finally, a tubercular or strumous diathesis seems to be as potent a factor in the causation of fistula as it is in other suppurative troubles. The appearance of a fistula in a tubercular subject is characteristic of the constitutional malady. It is thus described by Messrs. Alfred Cooper and F. Swinford Edwards:[42] "The part is, as a rule, unusually hirsute; the ischio-rectal fossæ are drawn in, owing to absence of fat; the sphincter is weak and offers no resistance to the introduction of the finger. The skin around the orifice is bluish and often considerably undermined, and the discharge is thin and watery. The internal orifice is often large, and the mucous membrane around it is also undermined."