{"id":50767,"date":"2017-08-16T04:56:54","date_gmt":"2017-08-16T10:56:54","guid":{"rendered":"http:\/\/www.featheredphotography.com\/blog\/?p=50767"},"modified":"2017-08-16T12:47:04","modified_gmt":"2017-08-16T18:47:04","slug":"the-supracoracoideus-an-ingenious-adaptation-for-flight-in-birds","status":"publish","type":"post","link":"https:\/\/featheredphotography.com\/blog\/2017\/08\/16\/the-supracoracoideus-an-ingenious-adaptation-for-flight-in-birds\/","title":{"rendered":"The Supracoracoideus \u2013 An Ingenious Adaptation For Flight In Birds"},"content":{"rendered":"

Occasionally I rerun a favorite older post because many current readers have never seen it. I’ve been wanting to rehash this one, originally published on November 14, 2013,\u00a0for some time so I could\u00a0fine-tune it and see if I could do a better job of explaining a fairly complex subject. I’ve rewritten much of the text, added a photo and edited the formatting.\u00a0<\/em><\/p>\n

When I was teaching high school zoology I was fascinated by the many adaptations of birds for flight. I still am.\u00a0One of them is a unique and fascinating\u00a0muscle arrangement that allows the return stroke of the wing after the powered downstroke\u00a0while still maintaining aerodynamic stability. I hope you\u2019ll allow me a little change in direction with today\u2019s post as I attempt to explain and illustrate one of the marvelous\u00a0anatomical adaptations of birds for flight.<\/p>\n

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\"\"<\/p>\n

The Problem:<\/strong><\/p>\n

The body of a bird basically hangs down\u00a0from the wings during flight. The wings attach high on the body for a reason\u00a0– the\u00a0huge and heavy\u00a0breast muscle (pectoralis) lies below that attachment so this arrangement provides a low center of gravity, prevents the bird from being top-heavy in the air\u00a0and provides\u00a0aerodynamic stability. The pectoralis (flight)\u00a0muscle attaches to the keel of the sternum and the humerus of the wing so when that muscle contracts it provides the\u00a0powered down-stroke of the wing.<\/p>\n

So\u00a0one of the dilemmas of bird flight is how to design a muscle arrangement\u00a0that will power the upstroke of the wing and still maintain that low center of gravity.\u00a0It\u00a0might seem\u00a0logical that the\u00a0muscle that would provide\u00a0the upstroke would be along the back but such an arrangement would place a relatively large muscle mass high on the body and above the wing attachment, raising the center of gravity and compromising aerodynamic stability.\u00a0Anyone who has ever eaten a chicken back knows that there’s very little meat (muscle) there which is evidence that natural selection came up with another solution.<\/p>\n

And that solution is truly\u00a0ingenious.<\/p>\n

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\"\"By L. Shyamal [CC-BY-SA-2.5 (<\/em><\/strong>http:\/\/creativecommons.org\/licenses\/by-sa\/2.5<\/em><\/strong><\/a>)], via Wikimedia Commons<\/em><\/strong><\/p>\n

The Solution:<\/strong><\/p>\n

In this graphic you can see how the contraction of the pectoralis muscle\u00a0would power the wing down. But beneath and lying next to the pectoralis is another muscle \u2013 the supracoracoideus (that word is a mouthful, I know – it means \u201cabove the coracoid\u201d bone). The supracoracoideus is antagonistic (a muscle that opposes another muscle – our biceps is antagonistic to our triceps)\u00a0to the pectoralis and provides the upstroke. It is attached to the upper <\/em>side of the humerus by a unique \u201crope and pulley\u201d arrangement\u00a0provided by\u00a0a tendon that travels up and over a notch in the scapula before attaching to the humerus. So even though the muscle is below the humerus, the direction of pull is from slightly above so that\u00a0when it contracts it raises the wing and aerodynamic stability is maintained by keeping the weight of the muscle down low.<\/p>\n

Most folks are very familiar with the supracoracoideus, they just don\u2019t know\u00a0its formal name.<\/p>\n

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 <\/p>\n

\"\"<\/p>\n

Chicken tenderloins or \u201ctenders\u201d are the supracoracoideus muscle of that domestic fowl. When we eat a chicken breast the supracoracoideus is the\u00a0smaller and more tender piece of meat lying between the larger mass of the breast (pectoralis muscle) and the bone. If you’ve ever cooked chicken tenders at home you\u2019ve likely noticed (and removed) the tendon coming off of\u00a0the coracoideus. That tendon is the one that wraps over the notch in the scapula,\u00a0attaches to the humerus and provides uplift to the wing. In this photo the tendon appears as a white stringy\u00a0cord coming out of the top of the\u00a0“tender”. You don’t want that little rascal\u00a0stuck between your teeth\u00a0(it’s tough as hell) so I always remove it before cooking.<\/p>\n

I realize this post won\u2019t be everyone\u2019s cup of tea but I\u2019m also aware that some\u00a0folks (me included)\u00a0like to know everything they can about their beloved birds.\u00a0This post is for you\u2026<\/p>\n

Tomorrow I\u2019ll get back to more standard fare.<\/p>\n

Ron<\/p>\n

Notes: The graphic above this last photo\u00a0is misleading in a couple of ways (it\u2019s the only appropriate Creative Commons graphic I could find). It shows a large space between the pectoralis and the\u00a0supracoracoideus, a space that does not exist. The two muscles actually\u00a0lie atop one another and are separated only by a very thin membrane.\u00a0The graphic also shows the\u00a0tendon to be as large in diameter as the muscle itself\u00a0when in reality the tendon is something like a narrow string coming out of the much larger\u00a0muscle as you can clearly\u00a0see in the last photo.<\/em><\/p>\n

Some may have also noticed the furcula in that graphic. The furcula is the “wishbone” but that’s a bird anatomy\/physiology lesson for another day. I’ve probably thoroughly confused\u00a0some of\u00a0my readers already.<\/em><\/p>\n

And yes, in answer to the obvious question, we’re having chicken tenders for dinner tonight…<\/em><\/p>\n

\u00a0<\/em><\/p>\n

 <\/p>\n

 <\/p>\n","protected":false},"excerpt":{"rendered":"

This is one of the marvelous anatomical adaptations of birds for flight.<\/p>\n

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