In this anatomy lesson, I’m going to cover the coccyx bone, also called the tailbone. Anatomists classify the coccyx bone as an irregular bone, and it makes up the inferior portion of the vertebral column, which is part of the axial skeleton.
Your tailbone does serve a purpose: It allows for the attachment of several muscles and ligaments, provides support for pelvic organs, and it stabilizes you while you’re sitting.
Coccyx Clinical Considerations
As a nurse or other healthcare professional, there are two quick facts you’ll want to know about the coccyx bone:
- If you have a patient who is immobile, the tailbone is one of those areas that you’ll want to monitor for pressure ulcers, just as Nurse Sarah indicated in our pressure ulcer video.
- When people break this bone, it can be extremely painful.
Coccyx Name Origin (Etymology) and Abbreviation
Because the coccyx has a triangular, pointed shape, it was named after the cuckoo bird’s beak. In fact, the word coccyx literally means “cuckoo” in the ancient Greek language.
As far as its abbreviation, anatomists label each vertebra with a letter and number. The individual bones of the coccyx are abbreviated as Co1, Co2, Co3, Co4, and Co5. This helps anatomists differentiate the individual coccyx bones from the cervical vertebrae (C1-C7).
In the average skeleton, the coccyx consists of 3-5 small vertebrae, which are often fused together in adults. However, in some adults, not all coccyx bones fuse together, and they can remain separate in 2 or 3 segments.
As I noted in my video comparing the male pelvis vs the female pelvis, the male coccyx tends to curve more toward the front of the pelvis, whereas the female coccyx tends to be straighter.
Coccyx Bony Landmarks and Structures
Now let’s take a look at some of the landmarks and structures on the coccyx bone, starting with the first coccyx bone (also called Co1).
- Coccygeal cornua: As you look at the superior (or top) portion of the coccyx, on the posterior (back) side, you’ll notice these two prominent tubercles that look like horns coming off the back, angling upward. These are called the coccygeal cornua, and they articulate (form a joint) with the cornua of the sacrum.
- Base: Next, there is an oval-shaped facet called the base, which allows for articulation with the apex of the sacrum above, forming the sacrococcygeal symphysis, an amphiarthrodial joint that allows only slight movement.
- Transverse process: On either side of Co1, you’ll notice a bony process extending out, which is called the transverse process. Transverse means “extending across,” and “process” means a projection. These processes meet the lateral edge of the sacrum, and they allow for the passage of the anterior aspect of the fifth sacral nerve.
- Lateral borders: The thin, lateral borders (side edges) of the coccyx allow for the attachment of muscles such as the gluteus maximus and coccygeus, as well as ligaments such as the sacrotuberous andsacrospinous ligaments.
- Coccyx surfaces: In addition to the two lateral borders, the coccyx also has two surfaces: an anterior (front) surface, which is concave (curved inwardly) and grooved, allowing for the attachment of muscles such as the levator ani; and it has a posterior (back) surface, which is convex (curved outwardly) and marked by tubercles such as the coccygeal cornua (see above).
- Apex: Finally, we have the apex, which is the inferior end of the coccyx bone. The word apex means something that forms a point. The apex of the coccyx is rounded at the tip but still comes to somewhat of a point when you look at the overall bone, and it allows for the attachment of the tendon of the external anal sphincter. The apex can be split into two portions in some people.
Free Quiz and More Anatomy Videos
Take a free coccyx anatomy quiz to test your knowledge, or review our coccyx anatomy video. In addition, you might want to watch our anatomy and physiology lectures on YouTube, or check our anatomy and physiology notes.