Posterior Torso Muscles, Part 2: Under the Radar

You may have noticed that I keep describing the forearm as the most difficult part of human anatomy to teach (and the most difficult to understand!) This area is so difficult for some pretty straightforward reasons: 1) There are so many forearm muscles, and 2) they all look very much alike. But sometimes I forget that the posterior torso muscles, although they are large and varied, are also among the most difficult to understand. In my class, they sometimes require as many days to get through as the forearm muscles. But the posterior torso muscles are confusing for a completely different reason-- unlike most muscles that concern the figure artist, they like to live under the radar.

Like most areas of the body, the posterior torso has several layers of muscle. When rendering most areas of the body, we artists tend to think primarily about the superficial muscle layers-- the ones that are visible at the surface and contribute most to the body's outward appearance. But things are a little different on the posterior torso. Its muscles are exceptionally broad, thin, and flat, which means we sometimes can see deeper muscles showing right through them. This is pretty cool, but it does make things a little more confusing.

In fact, sometimes the deeper muscles of the posterior torso show more clearly on the surface than the superficial muscles. How can that be? This happens because the superficial muscles are often so thin and flat that they just don't look like much on the surface. But the muscles underneath them are rounder and more defined, so it's actually easier to pick out their shapes. 

There are some wonderful examples of this in the figure renderings of Brian Skol. Brian is a student at the Ravenswood Atelier in Chicago, and during his time there he has developed a solid, stunning figure drawing technique and turned out an impressive collection of work. Brian also took my Anatomy course at AAA several years back, and while he is among several top students who mastered the class, he is distinctive in that he's the only one who's ever said the Anatomy final exam was not difficult enough! This comment was unexpected and refreshing, as I'm used to hearing just the opposite.

Several of Brian's figure drawings lovingly demonstrate the posterior torso landscape, but today (and in a few upcoming posts) we'll concentrate on this one. First let's look at the subtle ridges that help define the structure of the back.

Each of the skin ridges in Brian's figure drawing subtly reveals a muscular relationship on the posterolateral torso. Ridge 1 shows the point at which the latissimus dorsi meets the lumbar sheath. Ridge 2 demonstrates the furrow at which the external oblique muscle meets the rectus abdominis muscle. Ridge 3 shows where the serratus anterior muscle travels back toward its insertion on the underside of the scapula. (It's actually under latissimus dorsi at this point, but we can still see it because latissimus dorsi is so thin.) Ridge 4 shows the teres major muscle as it extends laterally toward the upper arm, where it will insert on the anterior side of the proximal humerus. The lower edge of teres major is hidden under latissimus dorsi, but it still shows. Finally, ridge 5 shows the posterior edge of the deltoid.

I know, I know. I did say subtle, right? But part of the beauty of the human body is that so much of it is a mystery; its structures are always there, doing their job, making things happen, but many don't necessarily need to be right in your face; they'd prefer to stay under the radar and let you discover them. 

So let's take a closer look at these shy little devils. The first step in this process was to block in some overall muscle shapes and a few bony landmarks, then to identify them.

Drawing in these basic structure shapes was the starting point for exploring each of the posterior torso ridges more closely. The iliac crest is shown in yellow but unlabeled. The large posterior torso muscles are trapezius (T) and latissimus dorsi (LD). Together with deltoid (D), they form a triangular window, in which we can see infraspinatus (Inf) and teres major (TM). Teres minor is barely peeking out between infraspinatus and teres major, but I didn't label it. Just anterior to latissimus dorsi, we can see two anterior torso muscles: external oblique (EO) and rectus abdominis (RA). I've also included some structures just under the iliac crest: Gluteus maximus (Gmax), gluteus medius (Gmed),  and tensor fasciae latae (TFL) all surround the greater trochanter of the femur (GT). Distal to that we can see vastus lateralis (VL) and the iliotibial band (ITB).

Now let's take a look at the ridges that are so beautifully and accurately rendered in Brian's drawing. We'll start with ridge number 1, where the lumbar sheath meets the latissimus dorsi muscle. First, here's how these structures look from a direct posterior view.

The lumbar sheath is a flat, diamond shaped aponeurosis covering a large portion of the lower back. It serves at an origin point for the large, bilateral latissimus dorsi muscles. We can often see a ridge along the lower back where these two structures meet. Note that both latissimus dorsi and the lumbar sheath have been removed on the right side of the body in this image.

You might recall this image from my first posterior torso post. At that time we looked at the relationships of the larger back muscles and the small triangular window they form (in which we can see some smaller muscles on the posterior surface of the scapula.) Now let's use this image to look at the landscape of the lower back. Occupying most of its space is the lumbar sheath, a diamond shaped aponeurosis (which is broad, flat, tendinous muscle covering.) The lumbar sheath serves as an origin point for the large bilateral latissimus dorsi muscles that run across the lower back and sides. Because the lumbar sheath is not muscle tissue, doesn't bulk up with use. So it can appear somewhat flat in comparison to the lumbar sheath. This means we can often see a ridge where these two structures meet. That's what we're seeing on the area labeled number 1 on Brian's drawing.

In this next image, the basic shapes of latissimus dorsi and the lumbar sheath are placed on top of Brian's rendering. This shows the placement of the individual structures and their meeting point. 

The lumbar sheath (shown in white) is an origin point for latissimus dorsi (LD). Because the lumbar sheath is flat and the latissumus dorsi has some bulk, we can often see a ridge on the back where the two meet. This ridge forms one of the upper edges of the lumbar sheath. The lower edges are formed by a small corner of the external oblique that reaches around to the back and attaches to the iliac crest.

We can see here that both the latissimus dorsi muscle and the external oblique form borders around the lumbar sheath. The angles of these borders give the lumbar sheath its diamond shape. On a more muscular individual, the flat lumbar sheath would stand out more obviously against the surrounding muscles and would become even more visible.

I am looking forwarding to explaining the other four ridges that can be seen in this lovely rendering, but this is getting a little long, so I'm going to sign off for now. I will cover ridges 2 through 5 in an upcoming post, and I'm also working on the rest of the elbow joint posts. See you soon! 

The Posterior Torso Muscles: Let's Go *Back* in Time. Get It?

Hello, all! My apologies for the long wait on this back muscle post, but my search for suitable posterior torso photos has been frustrating to say the least. Let's just say it's not easy to get friends, male or female, to pose topless for me. They're just not those kind of people. At least not since college. But my quandary serendipitously coincided with a massive office clean up during which I came across a dusty old hardbound book. The kind that you know used to have a paper jacket but now has only a cloth cover with gold embossed lettering. The title? Atlas of Anatomy for Artists. Copyright 1947, by Dover Publications, Inc. A true relic of the past!

You know the type of archaic artist's anatomy book I'm talking about-- one color printing on thick creamy paper, formal diagrams labeled entirely in Latin, black and white photos in which the models are haunted, anemic looking creatures with little black triangles covering up their genitalia. Or in which the genitalia are awkwardly airbrushed out so the model, no matter which sex, has the anatomy of a Ken doll. Or in which the model, wishing his or her identity to be hidden, is wearing some sort of blindfold, giving the whole thing a vague interrogation quality. This awkward modesty may seem quaint to us now, but back then it was a necessity. That type of anatomical detail would have earned a book a place in the XXX section of the local paperback grotto.

Is it an art anatomy book or a an advertisement for Interrogation Barbie and Firing Squad Ken? In 1947, it wasn't easy to tell the difference.

The quotes in this book are priceless. One reads "The anatomy of the female differs from that of the male in that the fatty tissue is better developed in the thighs and buttocks." Um, I guess that's one way of putting it. Another gem: "Plate 100 shows a well-built female with almost normal proportions." I'll bet that description made the model's day. Oh, Mr. Author, she might look completely normal if she didn't have one of your old gym socks tied around her eyes.

But I haven't gotten to the best part. Inside the front cover is the handwritten name of the original owner and her art school: Helen Davis, American Academy of Art, Chicago, Ill, 1950 – 51. My mom! Yep, my mom not only went to art school in the early 50s, but she went to the same school at which I teach anatomy today. I find this pretty cool.

My mom's name written in her first art anatomy book. Must ask her who this Buck person was. Did my father know about this?

In any case, the unearthing of this book from my 12 years of accumulated office junk came just in time. I've been wanting to do a post about back muscles, but I've been having a very difficult time finding photos that will show you all the visible surface landmarks. It turns out this book had several nice, clear (albeit archaic looking) posterior torso shots. I don't think they're quite enough, but we can at least begin here.

Shall we start with a quick overview?

On the left side of this figure, only the larger back muscles, trapezius and latissimus dorsi, are shown. We can also see the detoid, a large shoulder muscle on the side. The borders of these three muscles form a little triangular window through which three small muscles peek. Those muscles are not shown on the left side, however. On the right side we see them completely exposed. The blue dashed line indicates the triangular window through with they peek.

The posterior torso, like most areas of the body, is covered by several layers of muscle. But the surface landmarks her are a little more complicated than in other areas because the most superficial back muscles are so thin... and this means many of the deeper back muscles show at the surface as well. It's going to take more than one post to explain this, so we'll start today by looking at the superficial muscles only.

In order to become oriented on the back, it helps to find the largest muscles first and then move on to their smaller counterparts. The two largest muscles in the back (that, in fact, together cover most of the back) are the trapezius muscle and the latissimus dorsi. 

The trapezius is a diamond shaped muscle that covers most of the upper back. It's long midline origin attaches to nineteen vertebrae!-- C7 all the way down to T12. Its two lateral points attach to either scapula (the spine of each scapulae, to be specific,) its upper point attaches to the occipital bone on the posterior cranium, and its lower point attaches to the spinous process of the T12 vertebra.

The latissimus dorsi is a bilateral muscle that covers most of the lower back. It originates at the lumbar sheath, which attaches to the lumbar vertebrae and part of the sacrum. The latissimus dorsi's fibers converge as it travels upward toward its insertion on the proximal anterior humerus. As it reaches for the humerus it forms the back wall of an underarm depression called the axilla (which is more commonly known as the armpit.)

On this figure's right side, we can see the three posterior scapula muscles that peek through the triangular window formed by the larger muscles. These muscles are infraspinatus (whose name indicates its location inferior to the spine of the scapula) teres minor, and teres major. Teres minor, the smallest and deepest, tends to get squeezed out of the picture more often than not.

 The borders of the trapezius, the latissimus dorsi, and the deltoid (the large muscle on the shoulder) form a nice little triangular window on the posterior torso. Through this window peeks three smaller back muscles, infraspinatus, teres minor, and teres major. These muscles lie on the posterior scapula and are mostly used to adduct and rotate the upper arm. The key to finding these three posterior scapula muscles is first locating the triangular window formed by deltoid, trapezius, and the latissimus dorsi, and then looking inside it. 

Of these three posterior scapula muscles, the most superior (infraspinatus) and the most inferior (teres major) show most clearly, and they are the largest and most superficial. Teres minor, the smallest and deepest of the three, tends to get squeezed out of the picture. As a surface landmark, it often reads as a small crease or dimple between the other two.

Now let's try placing these on one of our 1947 models...

Man, just think. This is someone's grandpa now. Notice the long, diamond shaped tendinous floor of the trapezius, which itself can often be seen clearly as a surface landmark, particularly when you're as buff as this gentleman. Notice also that the lower tip of trapezius attaches to the spinous process of the T12 vertebra. Visible bony landmarks include the lateral end of the clavicle, the acromion process, spine, medial border, and inferior angle of the scapula,  and the iliac crest.

The muscles shown in the previous diagram are all shown bilaterally in this image. So we can see the larger muscles with their triangular window on both sides, as well as the posterior scapula muscles peeking through. Notice that the latissimus dorsi overlaps teres major a little bit. Keep in mind, though, that it does not obscure teres major, because it's so thin. If you're unable to locate the muscle windows in the above image, take a look at this:

In this image, only the muscle window has been given a color overlay. Infraspinatus, teres minor, and teres major peek through this window.

The blue area indicates the window formed by deltoid, trapezius, and latissimus dorsi. It's within this window that we can see infraspinatus, teres minor, and teres major. We will look at this more closely in our next post, as well as quite a few other visible muscles that I haven't even mentioned yet. Also, there is so much variation in the appearance of back muscles that I'd like to show a lot more photos! And, after all, there are lots more 1947 nudes to peruse. See you next time.