Wednesday, January 4, 2012

Sternocleidomastoid: Don't Forget the Cleido!

Just a quick landmark sighting today, and this time on an illustration instead of a photograph. We've already had a close look at the sternocleidomastoid muscle and its surrounding structures in an earlier post, The Anterior Neck: Theme and Variations. But this wonderful rendering by an old pal made me want to revisit Mr. SCM briefly. Shawn Campbell is a talented and prolific artist whose seemingly endless turnout of illustrations have been a great source of inspiration to me ever since we met in Ms. Brackman's seventh grade art class. Thirty-plus years later, Shawn and I continue to share our friendship, our ideas, our rants and, of course, our art, with one another.

One thing I like to stress in my anatomy class is that knowledge of human skeletal and muscular structure is not only useful when drawing realistically but also when drawing a human (or humanoid) with stylized or exaggerated features. Shawn's drawing below demonstrates this beautifully. Let's take a look:

This head drawing, and all of Shawn's figure and portrait studies, show his knowledge of the human form and his ease and comfort in rendering it. Even in this exaggerated head study, it's clear that Shawn understands the structure of the skull, the shape relationships of the external ear, and the nuances of the anterior neck muscles. One anterior neck muscle in particular, the sternocleidomastoid, caught my eye here.

The sternocleidomastoid muscle is named for its points of origin and insertion; its name has three parts (sterno-cleido-mastoid) because this muscle has two origin points and one insertion point. The sternocleidomastoid muscle's origin points are the superior edge of the sternum (sterno-) and the medial end of the clavicle (cleido-) and its insertion point is the mastoid process (-mastoid) which is a bony lump on the temporal bone than can be felt just posterior and inferior to the ear. The bilateral sternocleidomastoid muscles grab the mastoid processes and, among other actions, allow us to turn our head from side to side.

But or some reason, the poor clavicular origin point of the sternocleidomastoid muscle is too often neglected by figure and portrait artists. We all seem to know about the sternal attachment-- most likely because it's more visible-- and we tend to draw it very clearly (sometimes even too clearly.) But very often we completely leave out the clavicular attachment. Which is why I loved this rendering of Shawn's. He didn't forget the clavicular attachment! 

Let's look at the figure again below, but on this one (with Shawn's permission) I've added a little diagram:

The sternocleidomastoid muscle is a bilateral structure, meaning there are two of them-- one on either side of the body's midline. The two sternal attachments of the muscle connect to either side of the jugular notch at the superior edge of the manubrium of the sternum. (The jugular notch is also known as the suprasternal notch, as suprasternal means above the sternum.) This is the attachment we almost always remember to draw. 

The clavicular attachment, however, is often overlooked. As you can see here, it connects to the clavicle and it is generally wider and flatter than the sternal attachment. So from now on, don't forget to draw this lovely little portion of Mr. SCM!

One last note: Your common carotid artery runs right through the little split between the sternal and clavicular attachments of the sternocleidomastoid muscle. So press your finger in there if you want to feel your carotid pulse. Sometimes you can even see your carotid pulse on this spot. That's pretty cool.

Thanks so much to Shawn for letting me use his illustration. If you'd like to see more of Shawn's work, take a look here. I have another old school buddy helping me out with what I hope is the the next post, back muscles. See you then!

1 comment: