[Illustration: Fig. 2—Diagram of the Nervous Relations of Irritable Ulcer of the Anus (Hilton). _a_, ulcer on sphincter ani; _b_, filaments of two nerves are exposed on the ulcer, the one a nerve of sensation, the other of motion, both attached to the spinal cord, thus constituting an excito-motor apparatus; _c_, levator ani muscle; _d_, transversus perinæi muscle.] Andrews[7] directs attention to Hilton's diagram (Fig. 2), as showing that impressions from a fissure are carried to that part of the cord which supplies the pudic nerves and the ilio-lumbar, lumbar, and sciatics, which include the motor supply of the external sphincters as well as of the bladder and the lower extremities. From these general considerations we can understand why reflex spasm of the sphincter is so constant and important a sign of this malady, and how other and more general reflexes are to be accounted for,—such as symptoms of bladder and urethral diseases, radiating pains, etc. We also find in the nervous mechanism of the part an explanation of the predisposing causes, important symptoms, and pathology of this peculiar affection. As to the immediate origin of this lesion, it may be said to arise from a variety of causes, such as atony of the rectum, or other conditions leading to constipated habits. In these cases the bowel becomes impacted with hardened feces, which when discharged overstretch the delicate mucous membrane, and thus, either by irritation or by direct abrasion, the ulcer is formed.[8] In consequence of spasmodic or organic contraction of the external sphincter ani, fecal matter or some other foreign body lodges in the fossa between the two anal sphincters, and by its long-continued presence in this pent-up situation becomes highly irritating and gives rise to an obstinate fissure.[9] Anal fissure sometimes results from the excoriations produced by vitiated and acrid discharges, such as occur in dysentery, chronic diarrhœa, cholera, leucorrhœa, etc. Hemorrhoids are frequently a predisposing cause and a complication of this affection.[10] They narrow the outlet of the bowel, and through the successive inflammatory attacks to which they are subject the neighboring tissue loses its elasticity, is rendered brittle, and is easily lacerated. Polypi are not uncommon causes of this lesion.[11] The polypus is usually situated at the upper or internal end of the fissure, but it may be on the opposite side of the rectum, as in several cases coming under the author's observation. Allingham[12] states that ulcer of the rectum may result from a congenital narrowness of the anal orifice, being then usually seen in children; or it may be caused by an hypertrophied condition of the sphincters, which has arisen from severe constipation or some rectal affection.