Dissection - Muscles, vessels, nerves level 16
Description:
Up to this point in the dissection process, dissection has focused on the anatomy of the limbs with some work in the head region. To arrive at this stage, the dissection begins to focus on the wall of trunk, or body wall. There is a distinct muscle pattern in the wall of the trunk, which encompasses the neck, thorax, abdomen, and perineum. This pattern has two principal groups -muscles situated on the posterior aspect of the vertebral column (epaxial muscles) that are innervated by the posterior (dorsal) rami of spinal nerves and muscles anterior and lateral to the vertebral column (hypaxial muscles) that are innervated by the anterior (ventral) rami of spinal nerves.
The expaxial muscles are the extensor muscles of the vertebral column and are organized in distinct layers from superficial to deep. The hypaxial muscles form a distinct pattern of six muscles - an anterior strap of muscle in the anterior most wall of the body, a four-layered lateral wall that covers the side of the trunk from anterior to posterior, and a subvertebral muscle strap on the anterior aspect of the vertebral column. The four layers of the lateral body wall will be removed in succession during the next stages of the dissection. In this stage the outermost, or supracostal, muscle layer has been removed. Muscles from this outer lateral layer are some of the muscles the upper limb annexes to suspend the scapula from the trunk. The outermost lateral wall muscles removed in this stage are the annexed limb muscles - the levator scapulae and serratus anterior and the trunk muscles - the serratus posterior muscles along with the external lamina of the external oblique. Notice that on the left side some of the outer lamina of the external oblique has been left so that you can clearly observe the relationship between the more superficial outer lamina of the muscle and its deeper lamina. The outer lamina is the homologue of the serratus anterior in the thorax, while the deeper lamina is the homologue of the external intercostal. On either side of the body notice how the deeper lamina does not extend as far anteriorly as the more superficial lamina of the external oblique.
