Dissecting a Whole Chicken

Dissecting a chicken wing or chicken leg is a good way to observe limb anatomy. The wings and legs of chickens are readily available for their value as meat, and provide good analogs to human limbs. Whole chickens are just as easy to come by–why not dissect a whole chicken to investigate the muscles and bones of the torso? (Come to think of it, you could probably also dissect a turkey, a cornish hen, or a holiday duck, but I haven’t tried any of these myself.)

Unlike the limbs, the torso contains not only muscles and bones, but also internal organs. The muscles and bones of the torso form a sort of musculoskeletal casing, holding and protecting the package of internal organs inside. This is true of chickens as well as people. A butcher preparing a whole chicken usually removes the internal organs, since most people aren’t interested in eating them, but this still leaves the skeleton and musculature of the torso for study. (Some people like to eat the neck, heart, gizzard, and liver, and the butcher will often place these “giblets” back inside the bird before packaging, so you might not find the torso entirely empty.) A whole chicken from the supermarket looks like this:

A Whole Chicken

A Whole Chicken

Removing the skin from the torso of the bird is fairly easy. It separates easily from most of the front of the fowl, being tied down by fine ligaments in only a couple of places. These ligaments are easily cut. The skin is glued down tightly over the lower spine, and I just cut around it, leaving a patch of skin remaining over the lower spine. I also didn’t bother to remove the skin from the wings. My skinned bird looked like this:

A Skinned Chicken

A Skinned Chicken

Where is the best meat? Where are the biggest muscles? Most people like the breast meat best–the muscles there are the largest on the body, and free of bones or ligaments or gristle. Why would the muscles be the largest here? These are the flight muscles, the ones responsible for pulling the wings down. They correspond to the pectoral muscles of people, which perform a similar action on our arms.

If you examine any of the muscles closely, you will find fine stripes or lines running through the muscles. Perhaps you’ve noticed this when you are eating chicken–it tends to pull apart in threads or strips. Perhaps you’ve noticed that anyone who draws muscles draws them with stripes or lines running through them. When you are looking at the pinstripes in the chicken muscle, you are seeing that muscle is made up of threads or fibers. Muscle is fibrous.

You might also notice that not all muscle has exactly the same color. The flight muscles, the muscles it uses rarely and briefly but that have to be very powerful, are whitish. The legs of the chicken, the parts it uses more or less continuously all day long, are darker, a little closer to the color of blood. To a cook or a diner, the legs are “dark meat” and the breast is “white meat”.

White Meat and Dark Meat

White Meat and Dark Meat

Running down the center of the chest is a ridge of bone, a single bone in the center of the chest that corresponds to the sternum in humans. Actually, the ridge is only the end of a “keel” sticking out of the sternum. This keel provides something for the anchor end of the flight muscles to grab onto, and is a universal feature in birds. If you carefully slice the muscle free from the side of the sternum, you can discover two layers, corresponding to the pectoralis major and pectoralis minor in people. The pectoralis major flaps the wing down, as you can demonstrate by pulling on it. The pectoralis minor, also known as the supracoracoideus, supposedly gathers into a tendon that runs around the coracoid bone like a pulley, and pulls on the wing from the upper side, causing it to flap up. I tried to demonstrate this by pulling on the pectoralis minor in my chicken, but I couldn’t do it without tearing the muscle.

Flight Muscles

Flight Muscles

Running among the muscles of the body are fine wires, and tiny tubes. These are small, delicate, easy to damage, and hard to find. If you partially break open the largest joint in a chicken body–the hip joint–and carefully probe within the fold, you may be able to find short sections of these tubes and wires where they are especially large. The wires can be mistaken for tendons, and the name “nerve” comes from a Greek word for sinew or tendon. The tubes apparently carry blood–if you nudge the tube you can squish the blood back and forth a little. These are veins. (I’m fairly certain that they are not arteries, which are muscular and generally contract upon death, squeezing the blood out of them.)

Femoral Nerves and Vessels

Femoral Nerves and Vessels

If you can thoroughly clean a chicken without damaging the bones underneath, it will also present you with a nice “axial skeleton” example, or at least a torso skeleton. I broke off the wings and legs, thinking it would be much too tedious to try to clean the entire skeleton, and trimmed as much meat from the torso as I could with a knife and scissors. I then boiled the skeleton to soften the remaining meat, after which I could pry or gouge it from the bones with my fingers. This is the result:

The Axial Skeleton of a Chicken

The Axial Skeleton of a Chicken

First of all, notice that the overall structure is the same as that of a human: a ribcage on top, with some accessory bones where the wings attach, a “waist” in the middle, and a pelvis at the bottom to which the legs attach. One difference is that the “tailbone” in the chicken is actually long enough to make a tail. At the front of the ribcage is a single solid bone resembling, and named after, the human sternum. The difference between a chicken sternum and a human sternum is the gigantic “keel”, the ridge of bone projecting down the center, to which the powerful flight muscles anchor themselves. The sternum ends in a sharp, dagger-like, cartilaginous point. Try feeling the bottom of your own ribcage, and follow the ribs on each side as they rise towards the center and meet at the peak of the “thoracic arch”, which is also the lower end of the sternum. At this point you can find a similar pointy projection from the bottom of your own sternum. A name for these pointy tips that works well with children is “dagger bone”, but the official name is “xiphoid process”. (The “xiphoid” comes from a greek word for a certain sword which the sternum resembles, and the “process” refers to the fact that it is projecting or proceeding outward.) At the top of the ribcage you can find the wishbone, which corresponds to our own collarbones, or clavicles. The difference between the chicken’s wishbone and human clavicles is that in a human, the clavicles are separate and join the sternum on each side, whereas in the chicken they are fused to each other, and the junction is joined to the sternum by a ligamentary connection. Along the upper back are two flattish bones that correspond to the shoulderblades, or scapulae. There is another large stick-like bone in the shoulder which does not seem to correspond to a human bone, but by following the skeletal development in embryos, a correspondence can be traced to the coracoid. If a human scapula is a triangle with a claw on top, the coracoid is part of the “claw”.

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One Response to Dissecting a Whole Chicken

  1. Dei Gratia says:

    This is a useful page for someone trying to educate a budding vet in anatomy and surgery, and right along my own lines of explanation, but with much superior knowledge to mine. Thank you very much :)

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