Tail bone12/3/2023 Of these, the superior pair are the largest, and are called the coccygeal cornua they project caudally, and articulate with the cornua of the sacrum, and on either side complete the foramen for the transmission of the posterior division of the fifth sacral nerve. The posterior surface is convex, marked by transverse grooves similar to those on the anterior surface, and presents on either side a linear row of tubercles – the undeveloped articular processes of the coccygeal vertebrae. It gives attachment to the anterior sacrococcygeal ligament and the levatores ani and supports part of the rectum. The anterior surface is slightly concave and marked with three transverse grooves which indicate the junctions of the different segments. It has been shown that the coccyx may, in some people, consist of up to five separate bony segments, the most common configuration being two or three segments. Most anatomy books incorrectly state that the coccyx is normally fused in adults. The first segment is the largest it resembles the lowest sacral vertebra, and often exists as a separate piece the remaining ones diminish in size rostrally. All the segments lack pedicles, laminae and spinous processes. ![]() The transverse processes are most prominent and noticeable on the first coccygeal segment. ![]() In each of the first three segments may be traced a rudimentary body and articular and transverse processes the last piece (sometimes the third) is a mere nodule of bone. It articulates superiorly with the sacrum. The coccyx is formed of three, four or five rudimentary vertebrae. Structure A coccyx with four vertebrae below the sacrum It comprises three to five separate or fused coccygeal vertebrae below the sacrum, attached to the sacrum by a fibrocartilaginous joint, the sacrococcygeal symphysis, which permits limited movement between the sacrum and the coccyx. In animals with bony tails, it is known as tailhead or dock, in bird anatomy as tailfan. ![]() humans and other great apes) since Nacholapithecus (a Miocene hominoid), the coccyx is the remnant of a vestigial tail. The coccyx ( PL: coccyges or coccyxes), commonly referred to as the tailbone, is the final segment of the vertebral column in all apes, and analogous structures in certain other mammals such as horses.
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