Sunday, January 29, 2012

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.

2 comments:

  1. fantastic and clear, thank you so much!

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    1. Thank you very much! I'm glad you like it. I'm sorry it took me so long to publish this. For some reason I did not get a notification!

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