Muscles of the Chest

10/21-10/22

Focus Question:

Identifying the muscles of the chest: pectoantebrachialis, pectoralis major, pectoralis minor, xiphihumeralis, serratus ventralis and exterior intercostals.

Procedure:

1. Identify the striations of the pectoantebrachialis, pectoralis major, pectoralis minor and the xiphihumeralis the make an incision with the scalpel. Striations are a series of ridges, furrows or linear marks. For these muscles, identify the striations that run across the chest (these are the white lines that separate the different chest muscles). The pectoantebrachialis is superior (above) to the pectorals major. The pectorals major is intermediate between the pectoantebrachialis and the pectorals minor. The pectoralis minor is inferior (below) the pectoralis major. The xiphihumeralis is inferior (below) the pectoralis minor. Review the Anatomy booklet for further direction on the location of these superficial chest muscles.
2. Use the scalpel to cut around and under the chest muscles by cutting through the connective tissue. Do not completely remove the layer of muscle, leave it connected on the side (creating a flap) in order for the incisions and the placement of the different chest muscle to be identified.
3. Fold the flaps of muscle over and take a picture. Then take a picture with the flaps of muscle laid out in their original position.
4. Because the pectoralis minor and the xiphihumeralis was just separated from the chest, the serratus ventralis is now visible. Follow the striations and begin to separate this layer of muscle using the scalpel to cut through the connective tissue. Do not completely remove this muscle, leave it connected on the side (creating a flap) in order for the incision and the muscle’s location to be identified.
5. Underneath the serratus ventralis, are the exterior intercostals of the cat, which are now visible with the serratus ventralis muscle folded out of view. Take a picture with the exterior intercostals exposed (the serratus ventralis folded out of view) and take a picture with the serratus ventralis placed in its original position, covering the exterior intercostals.

Materials: Scalpel

Data and Observations:

All of Semara’s (the cat’s) chest muscles looked to be in great condition and were all in the correct position. Semara’s striations were clearly visible, making it easy to identify her chest muscles. The pectoantebrachialis, pectoralis major, pectoralis minor and the xiphihumeralis were all smooth and faint in color with small white striations. The serratus ventralis was darker in color while smooth and also had faint striations. The exterior intercostals were also darker in color and part of Semara’s ribs were visible and able to be felt through the exterior intercostals. Pictures of the data collected are shown below.

Human Corresponding Chest Muscles

Conclusion:

Removing the layers of muscle was challenging, at times I questioned if I was removing more than just muscle or if I wasn’t removing the correct muscle. I never knew how deep to cut and feared I would cut through something I wasn’t supposed too. Making incisions along the ends of each muscle helped me see the whole picture. I had a much better understanding of the different chest muscles once I could see the layers of muscle physically cut out and separated. Studying the chest muscles was a bit boring for me but I did appreciate the difference in texture and color between the different chest muscles.