“Anatomists called the intestine's final stretch straight, and it mostly is not.”
The Latin anatomists who named the rectum around the first century CE believed they were describing a self-evident truth: this section of the large intestine appeared straighter than the coiling mass above it. The full phrase was intestinum rectum, the straight intestine, drawn from the Latin adjective rectus, meaning right, upright, straight. Galen of Pergamon used the term extensively around 170 CE in his anatomical writings, and it entered the canon of medical Latin with his authority behind it. Modern imaging shows the rectum has two S-curves, but the name predates the technology.
Latin rectus had a life beyond anatomy: it produced erect, correct, direct, rector, and rule through various Romance and English paths. The root itself traced back to the Proto-Indo-European reg-, meaning to move in a straight line or to lead, which also gave Greek oregos and English right. Roman engineers used rectus to describe straight roads; grammarians used it for correct construction; physicians used it for the intestine they observed in dissection. The word carried institutional authority in every domain it entered.
Vesalius in 1543 included the rectum in his anatomical plates, showing its connection to the sigmoid colon above and the anus below. His illustrators depicted it with a modest curvature, though still significantly straighter-looking than the colon. Surgeons became intensely interested in the rectum in the nineteenth century as colorectal cancer became better understood. William Ernest Miles developed the abdominoperineal resection in 1908, a procedure that removed the entire rectum and anus for cancer, transforming proctology into a surgical specialty.
The word crossed from Latin anatomy into English medical texts in the seventeenth century and has never been challenged for a replacement. The rectum is roughly 12 centimeters long, stores feces before defecation, and is a common site for both benign polyps and malignant tumors. Colonoscopists examine it in every screening; proctologists specialize in its diseases; surgeons now remove it laparoscopically. The name is two thousand years old; the procedures to save it are largely from the last hundred.
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Today
The rectum is the final 12 centimeters of the large intestine, between the sigmoid colon and the anal canal, responsible for storing feces until defecation. It is one of the most examined structures in modern medicine: colonoscopy reaches it first, polyps are removed from it most often, and colorectal cancer screening targets it specifically. The word has survived precisely because it does the job.
That the rectum is not actually straight is a small irony Galen could not have anticipated. The curves became visible only with modern imaging. But the name stuck, because naming things after what they look like is ancient medical habit, and habit outlasts accuracy.
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