Thursday, May 3, 2012

The Annular Ligament: Full Circle!

It's a big day here today-- it's Human Anatomy For The Artist's first anniversary! Yep, it was one year ago today that the debut post, The Ventral Forearm: What are those Tendons? went live. Today, 366 days, 28 posts, and 80,314 page views later, I am happy to say that my goofy little blog is still going strong. As of this morning, Human Anatomy for the Artist has 89 Blogger followers, 51 Networked Blogs followers, and 2,032 Facebook followers. Writing and drawing about this topic is such a great joy, so I want to thank you for all the wonderful forms of encouragement, including your regular visits, words of gratitude, and messages from around the world. It's so gratifying to know that people are learning from these posts. Please keep spreading the word as we head into our second year!

Year 2 dangles many new post ideas before us; there are so many structures and concepts I still want to cover. It is quite awesome (and reassuring somehow) that a finite science like Anatomy can still have such vast depth. I can't imagine trying to write about a subject such as space or philosophy, whose possibilities are truly endless, without going a tad crazy.

The fact that we've come full circle today gave me the idea to write about an anatomical structure that also comes full circle. The annular ligament is named for its circular, or ring-like structure; the Latin word anulus means ring, so annular means "ring like." Quite fittingly this morning, both the words annual and anniversary come from a related Latin root; when an event is annual, it has come full circle from the previous year. Like the annular ligament, this blog comes full circle today. And even more fittingly, this structure was discussed in the very first post a year ago today.

Here is the image from that post again, with only the ligament and some related tendons labeled. Before going further, I should point that this particular annular ligament is not the only one in the human body. This name is given to most any ring-shaped ligament, and this is just one of at least five. As you can see, this one is located at the distal forearm. (Some of the others are located on the proximal radius, the ankle, the knee, and the trachea.)

The annular ligament in the wrist isn't something we artists think about much when we draw the human figure. You can't really see it on the surface. But it does affect surface appearance. There are two fairly visible tendons on the ventral wrist, the tendon of flexor carpi radialis and the tendon off palmaris longus. The tendon of palmaris longus is usually more visible than that of flexor carpi radialis because it runs outside the annular ligament. So if you're drawing the two ventral wrist tendons, it's important to make sure the correct one is more visible. Palmaris longus, the more visible of the two, is closer to the ulnar (pinky) side of the hand. This is explained in much more detail in the first post from one year ago, and some photographic and illustrative examples are shown there as well.

The function of the annular ligament on the distal wrist is to retain the position of the long forearm tendons that reach into the hand (with the exception of the palmaris longus tendon, whose distinction is its unique course outside the annular ligament.) This annular ligament's function is reflected in its more commonly used name, retinaculum. This term comes from the Latin retinere, which means to hold back.

Thank again for sticking around for the past year, and I look forward to working on upcoming posts! There are several series from the past year that need to be continued, including those on direction and location, back muscles, and the elbow joint. More in those series to come soon, plus more new material. See you soon!

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