Introduction

In this lab, you will explore the muscles of the gluteal region, posterior thigh, posterior leg, and plantar layers of the foot. Here are a few important tips before learning about these muscles:

• You should know the origins, insertions, actions, and innervations presented in the muscle charts for these and all muscles of the lower extremity. The muscle table is color-coded, and the information about what we expect you to know from the muscle table is described in the chart document itself. Please read that information. We will ask you questions about the function, attachment site, and/or innervation of muscles on the exam.
• We recommend using landmarks to understand the attachment sites, action, and sometimes the innervation as you are studying. Follow the muscle to its attachment site if it is visible. Notice the joint the muscle crosses and the side of the joint it is on, and that will give you information about the muscle’s action. In some cases, you can see the nerve go to or even through the muscle it innervates. These visual cues can help you remember the information from the muscle tables.

Lab Activity 1:  Visible Body Digital Atlas–Sacroiliac Joint, Pubic Symphysis, Coxal Joint

Explore the Sacroiliac joint and pubic symphysis: Click on the Systems icon, then under Skeletal System Views, click on 11. Pelvic Girdle. Using finger gestures, zoom, rotate, highlight and isolate to explore the sacroiliac joint between the sacrum and ilium and the pubic symphysis between the right and left pubic bones.

Explore the Coxal (hip) joint: Still in the Systems icon, then under Skeletal System Views, click on 11. Pelvic Girdle. First, observe the iliofemoral, ischiofemoral, and pubofemoral ligaments. Be sure to notice which bone of the pelvis they are attaching to, as this will tell you which ligament you are viewing. These ligaments all contribute to the capsule of the hip joint. They are difficult to see in images or on a donor, as the fibers all blend together. Therefore, you would only be asked to identify them on an image of the app. If you remove/hide the ligaments of the hip and the femur, you can now see the acetabulum, the articular surface of the os coxae. Also, observe the ligamentum teres, or ligament to the head of the femur. This ligament contains the artery to the head of the femur.

Explore muscles of the gluteal region and posterior thigh: Click on the Systems icon, then under Muscular System Views, click on 17. Hip. Explore all of the gluteal region and posterior thigh muscles provided in the list of terms for this lab. As you navigate through, highlight the various muscles, and use your muscle charts to study the origins, insertions, and actions of these muscles with the images.

While you are looking at the muscles of the hip, you can select the individual muscles, then click the red attachment icon. When you have clicked the attachment icon, videos will often pop up to demonstrate the motion of the muscles you have selected. You can also go to the Muscle Actions icon from the home page and scroll down to see the motions of the gluteal and thigh region. Explore the various movements at the hip joint in relation to the muscle actions responsible for those movements. You should also review these muscle actions from your muscle charts.

Explore the muscles of the leg: Click on the Systems icon and then Muscular System Views. Go to 19. Ankle and Foot. Use the right leg to view the muscles of the leg. Use finger gestures, rotation, zoom, and highlight tools to explore the muscles of the leg in the list of terms. Reference the muscle charts for origin, insertion, and innervation information. You will need to hide or remove the superficial muscles to see the deeper muscles of the leg.

Explore the muscles of the foot: Use the right leg to view the muscles of the foot. Use finger gestures, rotation, zoom, and highlight tools to explore the muscles in the list of terms. Some of these muscles are difficult to see on the dissected tissue, so be sure to observe all of the muscles of the foot using this resource. You will need to hide or remove the superficial muscles to see the deeper muscles of the foot.

Animations and Muscle Movements: While looking at the muscles of the leg and foot, you can select the individual muscles and then click the red attachment icon. When you have clicked the attachment icon, videos will often pop up to demonstrate the motion of the muscles you have selected. You can also go to the Muscle Actions icon from the home page and scroll down to see the leg and foot motions. Explore the various movements at the ankle and foot joints in relation to the muscle actions responsible for those movements. You should also review these muscle actions from your muscle charts.

Lab Activity 3: Navigator-Hip, Gluteal Region and Posterior Thigh

Use the navigator to examine the hip, gluteal region, and posterior thigh.

• First, identify the gluteus maximus on the 3D printed model.
• On the computer model, click on “Advanced” in the View window. Highlight “Muscles” in the first column. In the next two columns, you can add and remove muscles. Remove the muscles of the trunk and add the muscles of the gluteal region and lower extremity. You may want to remove some layers just on one side to compare the deep and superficial muscles or examine the muscles and their attachment points. Note that some of the muscles of the thigh will be cut off in the images. However, this is still a good opportunity to view the origins of several posterior thigh muscles.
• With all muscles removed, examine the ligaments stabilizing the hip joint.
• Also, observe the head of the femur, the gluteal muscles, and medial thigh muscles in the cross-sections.

Lab Activity 4:  Lower Extremity Donor Tissue-Limbs, Donors, and Plastinates

We have four wet tissue lower extremities for you to examine in this unit. Some are dissected so that you can view deep muscles, while others are dissected more superficially. Some of the muscles have been cut, but you can still observe most of the distal portion of the muscle in most cases. Some of the extremities contain a portion of the pelvis, while the others begin proximally at the femoral head.

We also have two plastinated specimens for you to examine in this unit. One contains more superficial muscles, while the other is a deep dissection also showing the neurovascular structures. You should try to find all structures on both wet and plastinated specimens, though some will not be visible on each specimen.

**Reminder: Never touch the plastinated specimens with wet gloves! Also, though you can turn the plastinated specimens to view different structures, you should try to handle these as little as possible. 

• Gluteal region: In the gluteal region, first observe the gluteus maximus. This is the largest and most superficial of the gluteal muscles. Just deep to this is the gluteus medius. The gluteus minimus is the deepest of the gluteal muscles. The piriformis is an important lateral rotator of the hip. There are five other small lateral rotator muscles of the hip. While they are listed in the muscle chart, you will not be asked to identify these muscles in class.
• Explore the muscles of the posterior thigh. The posterior thigh muscles are collectively called the hamstring muscles. The hamstring muscles originate on the ischial tuberosity. Two muscles travel to the medial aspect of the knee. The semimembranosus has a thicker muscle belly and a shorter tendon. The semitendinosus has a thinner muscle belly and a longer tendon. It sits just superficial to the semimembranosus. The biceps femoris has two heads. The long head of biceps femoris originates on the ischial tuberosity, but the short head of biceps femoris originates on the femur.  The two heads merge into a common tendon and insert onto the fibular head.

• Superficial posterior compartment of the leg: The most superficial posterior leg muscle is the gastrocnemius. It has a medial and lateral head that cross the knee to insert on the femur. This muscle aids knee flexion and is the primary plantar flexor of the foot. The soleus sits deep to the gastrocnemius and originates on the tibia. The gastrocnemius and soleus tendons merge to form the calcaneal (Achilles) tendon. The plantaris is a small muscle with a tiny belly deep to the gastrocnemius and a long, thin tendon extending toward the calcaneus. This muscle is not present in all individuals. You may not see it in this tissue, but it is visible in images.

• Deep posterior compartment of the leg: There are four muscles of the deep posterior compartment of the leg. The tibialis posterior runs along the posterior aspect of the tibia and acts to plantarflex and invert the foot. Flexor digitorum longus tendons extend to digits 2-5 and flex these digits. Flexor hallucis longus originates on the posterior fibula, and its tendon wraps around the medial aspect of the ankle before it reaches the distal great toe. This long path gives the muscle a mechanical advantage and makes it a powerful flexor of the first digit. The muscles Tibialis posterior, flexor Digitorum longus, and flexor Hallucis longus usually travel in a specific order around the medial malleolus. You can remember the order of these tendons using the mnemonic Tom, Dick, an Harry; “an” stands for posterior tibial Artery and tibial Nerve. Tibialis posterior is most anterior/superior, and flexor hallucis is most posterior/inferior.

The last muscle of the posterior compartment of the leg is the popliteus. This muscle is difficult to see on the tissue, but you can see part of it on the deep dissections. It sits on the superior aspect of the tibia and crosses the knee joint. It functions to medially rotate the tibia and “unlock” the knee from full extension in the first few degrees of flexion.

• Intrinsic muscles of the foot: The intrinsic muscles of the foot are muscles that act on the foot and are entirely located within the foot. The muscles that we just examined in the leg would be considered extrinsic muscles of the foot. The plantar aspect can be divided into four layers containing ten muscles or categories of muscles. You will not be asked which muscles are in a given layer. However, organizing the muscles into four layers can be helpful when studying the muscles.
  • Plantar fascia: This thick layer of fascia is superficial to the muscles of the plantar aspect of the foot. It has been cut in both wet specimens, but you can observe how it would attach to the calcaneus in anatomical position. This fascia can become inflamed with plantar fasciitis.
  • Plantar muscles layer 1: The flexor digitorum brevis muscle is deep to the plantar fascia and flexes digits 2-5. The abductor hallucis is the large muscle on the medial aspect of the great toe. It abducts the great toe. Likewise, the abductor digiti minimi is located on the lateral aspect of the 5^th digit and abducts that digit.
  • Plantar muscles layer 2: The muscles of this layer attach to the tendon of flexor digitorum longus. Quadratus plantae runs from the calcaneus to the tendons of flexor digitorum longus to adjust the angle of pull of these tendons. Because the flexor digitorum longus runs around the medial malleolus, without the adjustment from quadratus plantae, this muscle would cause the toes to flex in a medial direction. The quadratus plantae aligns these tendons so that the toes flex within the sagittal plane. The lumbricals of the foot are similar to those of the hand. They insert on to the flexor digitorum longus tendons distally and flex the MP and extend the PIP and DIP joints.
  • Plantar muscles Layer 3: The adductor hallucis is similar to the adductor pollicis of the hand. It is “7” shaped, with transverse and oblique heads, and it adducts the great toe. The flexor hallucis brevis and flexor digiti minimi muscles flex the great toe and 5^th digit, respectively. These muscles can be observed on the deep dissection.
  • Plantar muscles layer 4: The deepest layer of muscles on the plantar aspect of the foot is composed of the dorsal and plantar interossei. The Dorsal interossei Abduct the toes, while the Plantar interossei Adduct the toes (DAB and PAD). There are similar muscles with the same actions in the hand. However, be sure not to mix up the name of these muscles with those of the hand! In the foot, the interossei that adduct are called the plantar interossei, while in the hand, they are the palmar interossei. These muscles cannot be seen on the dissected tissue, but they can be observed in atlas images.