lab14
lab15
 
Schedule

Lab 14 - Gluteal Region & Posterior Thigh

Suggested readings from
Gray's Anatomy for Students, 2nd ed.
Ch. 6: 512-525; 547-554; 555-599; 628-637

Suggested readings from Langman's Medical Embryology

11th ed: Ch 9 pp 134-42 -- Ch 10 pp 147-54
12th ed: Ch 11 pp 145-50 -- Ch 12 pp 151-61

Prelab: Osteology of the Pelvis and Femur

Lab 14 Primary Lab Objectives:

  1. Locate the anatomical surface landmarks on the hip, thigh, and leg.

  2. Remove the skin on the posterior surface of the lower limb down past the knee, noting the presence of the cutaneous nerves and veins.

  3. Note the attachments of the tensor fascia latae and gluteus maximus muscles to the iliotibial tract.

  4. Reflect the gluteus maximus muscle and locate the piriformis muscle. Examine the relationships of the superior and inferior gluteal nerves and vessels to the piriformis muscle as they exit the greater sciatic foramen.

  5. Identify the gluteus medius muscle and transect the muscle to expose the underlying gluteus minimus muscle.

  6. Locate the deep muscles of the gluteal region: obturator internus, gemellus superior, gemellus inferior, quadratus femoris, and obturator externus.

  7. Locate the sciatic nerve; transect the gluteus maximus muscle lateral to it.

  8. Identify and trace the hamstring muscles from their common origin to their insertions.

 

Dissection Instructions

1. SURFACE ANATOMY: ANTERIOR THIGH AND LEG

  1. Locate the medial and lateral epicondyles of the distal femur (they are less pronounced than at the elbow but still palpable; check a skeleton) on the cadaver.
  2. Locate the patella on the cadaver.
 

 

  1. Measure one hand's breadth posterior to the medial edge of the patella to locate the great saphenous vein on the cadaver.

Atlas Images:

 

  1. On the lateral side of the leg of your cadaver, palpate the bony prominence below the lateral femoral condyle and mark it as the head of the fibula.

Atlas Images:

FUNCTIONAL ANATOMY

Identifying the fibular head under the skin on the lateral side of the knee is important because this landmark represents the position where the common fibular nerve enters the anterior leg in a position vulnerable to injury. This nerve is injured commonly at this location by compression against the fibula.

 

  1. At the ankle of the cadaver, locate the medial malleolus of the tibia and the lateral malleolus of the fibula.
  2. Mark the location of the dorsalis pedis artery. The dorsalis pedis artery is the continuation of the anterior tibial artery on the dorsum of the foot between the medial and lateral malleoli. This artery is often used to evaluate peripheral pulses.

Atlas Images:

 

 

2. GLUTEAL REGION

FUNCTIONAL ANATOMY:
The gluteal muscles are innervated by nerves that leave the pelvis through the greater sciatic foramen.

Atlas Images:

 

 

  1. Skin the gluteal region and the posterior thigh down to the knee.
 

 

  1. Notice the cutaneous nerves you are cutting through as you skin the gluteal region.
  2. You can identify these as cutaneous branches of dorsal rami innervating the fat-laden skin of the buttocks.
  3. Remove the extensive fat overlying the gluteus maximus muscle and note the muscle's lower edge crossing the fold under the buttock obliquely.
  4. Locate the specialized band of fascia of the thigh called the iliotibial tract. Its attachments are implied by its name.
  5. Trace the tensor fasciae latae and part of the gluteus maximus muscle to their insertions into the iliotibial band.

Atlas Images:

FUNCTIONAL ANATOMY:

The gluteus maximus muscle originates from 1) the back of the iliac crest, 2) the lower sacrum, and 3) all the dorsal ligaments binding the pelvis and sacrum together. It inserts into the iliotibial tract and the gluteal tuberosity of the femur. The gluteus maximus muscle lies directly behind the hip and acts primarily as an extensor of the hip joint. Notice that based on its attachments, it can also laterally rotate the thigh and tighten the iliotibial band. It is not active in walking since little active extension of the hip is involved but it comes into play in activities such as climbing stairs, rising from a squatting position, and running.

 

 

3. ILIOTIBIAL TRACT

  1. Verify that the superior and superficial fibers of the gluteus maximus muscle insert into the iliotibial tract.
  2. The smaller tensor fasciae latae, like the gluteus maximus muscle, also attaches to the iliotibial tract.
  3. Reflect the gluteus maximus muscle laterally toward the greater trochanter of the femur.
  4. Note the bursa that lies between this muscle and the greater trochanter.

NOTE: Cut the gluteus maximus carefully so that you don’t inadvertently take any fibers from the gluteus medius muscle below it. Some fibers of the the gluteus maximus attach to the iliotibial tract, which is a tight band of fascia on the lateral part of the thigh. Try to keep this structure intact.

Atlas Images:

Functional Anatomy:

The head of the femur lies medial to the axis of the shaft. This produces bending stresses in the femur and tends to bow it outward laterally. This tendency is resisted by the functional importance of the iliotibial tract and the muscles pulling on it. The tract also improves the leverage of the gluteus maximus and tensor fasciae latae muscles in rotating the thigh medially and laterally.

 

4. PIRIFORMIS MUSCLE

  • Reflect the gluteus maximus, working lateral to the sciatic nerve to avoid damaging the inferior gluteal nerve.
  • Define the medial edge of the greater sciatic foramen.
  • The little piriformis muscle emerges from this foramen.
  • Below the piriformis muscle, the inferior gluteal nerve and artery exit through the foramen to the gluteus maximus muscle. The sciatic nerve also exits the greater sciatic foramen below the piriformis muscle.

NOTE: Sometimes the sciatic nerve splits into the fibular nerve and tibial nerve early and the tibial branch can run through the middle of piriformis or exit the greater sciatic foramen above the piriformis muscle. See if your cadaver has one of these variations.

  • Above the piriformis muscle, the superior gluteal nerve and artery exit through the foramen to the gluteus medius & minimus and tensor fasciae latae muscles.

NOTE: Identification of the piriformis muscle will help to orient you in the gluteal region and find and identify the other rotators of the hip.

Atlas Images:

 

 

5. GLUTEUS MEDIUS AND MINIMUS

 
  1. Outline the gluteus medius muscle, noting its origin and insertion.
  2. Transect and reflect the gluteus medius muscle. This will expose the gluteus minimus muscle, which is immediately deep to it.

NOTE: It is often difficult to separate the fibers of the gluteus medius from the gluteus minimus. Dissect carefully in this area.

  1. Trace the superior gluteal vessels and nerves running across between the two muscles, supplying them and ending in the tensor fasciae latae muscle.

Atlas Images:

 

 

6. “LATERAL ROTATORS”: PIRIFORMIS, SUPERIOR AND INFERIOR GEMELLUS, OBTURATOR INTERNUS, QUADRATUS FEMORIS, AND OBTURATOR EXTERNUS.

A group of small muscles including both elevators and depressors cross the hip joint dorsally to act as lateral rotators of the femur:

  • Piriformis: the only elevator in this group.
  • Quadratus femoris
  • Obturator internus
  • Gemelli (L. ="little twins," diminutive of gemini)
  • Obturator externus

 

  1. Separate the lateral rotators, beginning with the piriformis muscle.
  2. The piriformis muscle, which you located earlier, is just below the gluteus minimus muscle and exits the greater sciatic foramen.
  3. The next three muscles (in order from superior to inferior) are: the superior gemellus, obturator internus, and inferior gemellus muscles.

Hint: You will not see obturator externus yet.  That will be visible from this aspect shortly when you transect quadratus femoris later.

  1. The quadratus femoris muscle is a square muscle that can be found inferior to the last three.

HINT: It is sometimes hard to see these small deep muscles.  Here we provide a description of where these small muscles originate and insert to help orient you to this complex region.  The piriformis muscle originates from the anterior surface of the sacrum and exits through the greater sciatic foramen to the greater trochanter. The quadratus femoris muscle runs from the ischial tuberosity to the back of the femur. The obturator internus muscle originates from the deep surface of the obturator membrane covering the obturator foramen and forms part of the lateral wall of the ischioanal fossa. Its tendon exits dorsally through the lesser sciatic foramen, which is the "door" to the ischioanal fossa. The gemelli muscles originate from the margins of the lesser sciatic foramen. These four muscles have separate little motor nerves from the lumbar plexus.

Atlas Images:

 

  1. Carefully transect the quadratus femoris muscle as shown by the dotted line in the diagram below to see the tendon of the obturator externus muscle wrapping around the hip joint posteriorly.
  2. Follow the pudendal nerve and accompanying vessels around the dorsal edge of the sacrospinous ligament into the ischioanal fossa.
  3. Trace the obturator internus muscle back again in the other direction from its origin to its insertion noting the bursa lying between its tendon and the body of the ischium.

Atlas Images:

FUNCTIONAL ANATOMY:

The five lateral rotators can be assisted in their task by the much larger gluteus maximus muscle.

 

 

7. SCIATIC NERVE

  1. With the cadaver positioned to allow a view of the interior of the pelvis, trace the sciatic nerve from the lumbosacral plexus to the greater sciatic foramen.
  2. Turn the cadaver over and look for this nerve as it runs down the thigh under cover of the hamstrings.

Atlas Images:

FUNCTIONAL ANATOMY:

The sciatic nerve contains both anterior and posterior divisions of the lumbosacral plexus. The anterior-division fibers run in the medial side of the nerve and become the tibial nerve. The posterior-division fibers run in the lateral side and become the common fibular [=peroneal] nerve. You should note that Nomina Anatomica has decreed the Latin form "fibular" to be preferred over the Greek "peroneal". Therefore, we will follow this usage. Keep in mind however, that many clinicians (and some anatomy professors) will persist in using the older term, "peroneal."

 

 

8. HIP EXTENSORS

  1. Identify the hip extensors (hamstrings): the biceps femoris, semitendinosus, and semimembranosus muscles.

Atlas Iamges:

FUNCTIONAL ANATOMY:

The hamstrings are depressor musculature (roughly corresponding to the biceps brachii muscle in the arm). They receive motor branches from the medial (tibial) edge of the nerve. An exception is the short head of biceps femoris, which is not really a hamstring, but an isolated elevator muscle that inserts with the long head of biceps femoris. The short head is therefore innervated by the posterior-division fibers from the lateral side of the nerve. The hamstrings can flex the knee and extend the hip joint. In walking, they contract extending the hip joint as the heel touches the ground, and flexing the knee as the toes leave the ground.

 

  1. Trace the hamstrings from their common origin on the ischial tuberosity to their insertions.
  2. Then sever and reflect the hamstrings, noting and cutting their motor nerves.
  3. Look for the bursa underlying the insertion of the semimembranosus muscle.
  4. Leave the short head of the biceps femoris muscle and the sciatic nerve intact.

NOTE: the semimembranosus and semitendinosus can be distinguished by the fact that the semitendinosus has a long thin tendon distally which lies on top of the semimembranosus muscle.

 

 

Lab 15 - Anterior Thigh & Leg

Suggested readings from
Gray's Anatomy for Students, 2nd ed.
Ch. 6: 555-599

Suggested readings from Langman's Medical Embryology

11th ed: Ch 9 pp 134-42 -- Ch 10 pp 147-54
12th ed: Ch 11 pp 145-50 -- Ch 12 pp 151-61

Lab 15 Primary Lab Objectives:

  1. Remove the skin from the anterior thigh and leg to the ankle and locate and examine the great saphenous vein. Understand the role of the valves in the veins of the lower limb.

  2. Examine the iliopsoas and consider the muscles that fuse to form it.

  3. Examine the femoral triangle containing the femoral artery, vein, nerve (and its branches), and lymphatic channels. Transect and reflect the sartorius muscle, exposing the saphenous nerve and the femoral vessels in the subsartorial canal. Examine the quadriceps femoris and consider the muscles that form this group and their action on the patellar ligament on the tibia.

  4. Locate the profunda femoris branch of the femoral artery and consider the arterial supply of the adductor muscles.

  5. Identify the extensor and depressor compartments of the leg; trace the path of the fibular nerve, expose and examine the extensor musculature.

  6. Trace the motor branches of the tibial nerve to the gastrocnemius muscle, and appreciate this muscle's insertion and action at the calcaneal tendon. Trace the arterial supply to the leg and expose the flexor muscles deep to the intermuscular septum.

 

Dissection Instructions

1. SKIN, FASCIA AND CUTANEOUS VESSELS

  1. Remove the skin of the the thigh and leg down to the ankle.

 

  1. Identify and dissect out the major cutaneous veins (especially the great saphenous vein) embedded in the superficial fascia.

 

  1. Cut the great saphenous vein about two inches below where it enters the femoral vein.
  2. Remove a six inch section of the great saphenous vein.

 

  1. Open the section of the great saphenous vein that you removed and wash it out in the sink to examine its valves.

FUNCTIONAL ANATOMY:
Veins have a limited muscular layer.  The valves in this and other veins in the lower limb prevent blood from pooling in the lower limb.  The great saphenous vein is often used for vascular bypass elsewhere in the body.

 

  1. Identify the deep fascia of the thigh: the fascia lata.
  2. Note that the iliotibial tract is continuous with the lateral intermuscular septum that marks the lateral boundary between the “elevators” and the “depressors” in the thigh.

HINT: You can locate the medial boundary between the elevators and depressors by lifting up the sartorius muscle.

Atlas Images:

 

2. HIP FLEXORS: ILIACUS, PSOAS MAJOR AND MINOR MUSCLES

FUNCTIONAL ANATOMY:
The iliopsoas muscle is composed of two separate bellies: the iliacus muscle has a fleshy origin from the iliac blade; the psoas major muscle originates from the vertebral column below the last rib. The two muscles pass over the rim of the pelvis, under the inguinal ligament, to a common insertion on the lesser trochanter of the femur. On the surface of the psoas major, you may be able to see the small psoas minor muscle (absent in about 40% of humans) running down to attach to the rim of the pelvis at the psoas major muscle's medial margin. Both the iliacus and psoas major muscles receive their innervation from the posterior divisions of the ventral rami L.2-4, which come together more laterally to form the femoral nerve.  The iliopsoas muscle is an important thigh flexor that helps initiate the swing of the limb.

  1. Locate the broad, fleshy fibers of the iliacus muscle on the inner surface of the ilium.
  2. Look for the longitudinal fibers of the psoas major muscle medially.
  3. Find the femoral nerve as it emerges from behind the psoas major muscle and runs down the surface of the iliacus muscle, enclosed within the iliac fascia.

A smaller nerve also running along the surface of the iliacus muscle, lateral to the much larger femoral nerve, is the lateral cutaneous nerve of the thigh.

Atlas Images:

 

  1. Follow the iliopsoas muscle towards its common insertion; here, you will find the femoral vessels.
  2. Push aside the femoral vessels and further expose the femoral nerve, which breaks up at this point into a cluster of motor branches to the extensors of the knee.

Atlas Images:

 

 

3. THE SARTORIUS AND QUADRICEPS GROUP: RECTUS FEMORIS, VASTUS LATERALIS, MEDIALIS, AND INTERMEDIUS MUSCLES

The femoral triangle is formed by the sartorius muscle laterally, the adductor muscles medially, and the inguinal ligament superiorly. Here, you will find three important structures passing under the inguinal ligament and into this triangle: the femoral artery and vein, and the femoral nerve.

  1. Identify the femoral artery and its branches superficial to the accompanying veins.
  2. Notice that fascia forms a femoral sheath around the artery and vein.
  3. Confirm that the femoral nerve is not contained in the sheath. Instead it runs around the inside of the pelvis superficial to the fascia of the iliacus muscle.

NOTE: the femoral nerve splits into many branches once it passes beneath the inguinal ligament. These include cutaneous sensory nerves as well as muscular branches going to the quadriceps group and pectineus.

 

 

  1. Identify the sartorius and rectus femoris muscles.
  2. Trace the sartorius muscle from origin to insertion, and compare its path with that of the rectus femoris muscle.
  3. Verify the actions of the sartorius muscle by pulling on it.
  4. Transect the sartorius muscle and reflect it to its attachments at either end.

FUNCTIONAL ANATOMY:
The sartorius muscle tends to rotate the femur laterally and flex the hip and the knee - bringing the hind limb into a position for sitting cross-legged on the ground. The origin and insertion of the sartorius (anterior superior iliac spine to the pes anserinus on the tibia) are close to those of the rectus femoris muscle (anterior inferiori iliac sine to the tibia via the patellar tendon) but the course of sartorius takes it behind the axis of rotation at the knee joint. Therefore, it acts as a weak flexor of the knee. It is part of this muscle group with the quadriceps, and is innervated by the femoral nerve.

 

  1. Identify the muscles that form the quadriceps femoris muscle group: the rectus femoris, and vastus muscles.
  2. Transect the rectus femoris muscle at mid-thigh, reflect it, and identify the three vastus muscles.
  3. At this point you may wish to transect and reflect the tensor fascia lata and gluteus minimus muscles to examine their cross-section more thoroughly.

Atlas Images:

 

  1. Trace the rectus femoris muscle back to its tendon of origin.
  2. Find the patellar ligament through which the quadriceps femoris muscle group attaches to the tibia via the patella, and define its insertion.
  3. Examine the vastus lateralis and medialis muscles and consider their attachments to the patella. 
  4. Thinking about the mechanics of their action, consider how they will move the patella.   
  5. Look at this on both a male and a female cadaver.
  6. Separate the adductor muscles from the vastus medialis muscle and expose the femoral vessels and nerve.
  7. Find the profunda femoris branch (="deep femoral a.") of the femoral artery, and trace it into the adductor group.

Atlas Images:

 

 

4. THE ADDUCTOR GROUP: ADDUCTOR LONGUS, BREVIS, AND MAGNUS, GRACILIS AND PECTINEUS MUSCLES

  1. Locate the saphenous nerve between the adductor and quadriceps muscle groups. The saphenous nerve is a major cutaneous branch of the femoral nerve traveling down the thigh in company with the femoral vessels.

HINT: To follow the saphenous nerve you will have to trace it through some muscular spaces. The saphenous nerve continues down and becomes cutaneous just below the knee. The vessels pass through a gap, called the adductor hiatus, between the insertions of the adductor and hamstring parts of the adductor magnus muscle to enter the popliteal fossa behind the knee.

Atlas Images:

  1. Beginning within the pelvis, trace the obturator nerve from the lumbar plexus through the obturator foramen and canal into the adductor muscle group. The artery accompanying the nerve is the obturator artery.

Atlas Images:

  1. In the medial thigh, identify the adductor longus muscle - This is the most superficial of the adductors.
  2. Look for the profunda femoris artery where it passes backward between the adductor longus and the pectineus muscles.
  3. Locate the perforating branches of the profunda femoris artery supplying the muscles attached to the linea aspera.

Branches of the profunda femoris artery supply the quadriceps muscle group, and the muscles on the back of the thigh.

  1. Sever the adductor longus muscle and reflect it to expose the adductor brevis and magnus muscles.

HINT: The insertion site on the femur of adductor brevis is directly beneath that of pectinus. Both are deep to adductor longus.

Atlas Images:

 

  1. Idenfiy the gracilis muscle (the most medial adductor,) the long, strap-like muscle along the inner thigh.
  2. Note the medial fibers of the adductor magnus muscle inserting into the adductor tubercle just above the medial epicondyle of the femur.

Atlas Images:

FUNCTIONAL ANATOMY:
The nervous innervation of the muscles found in the thigh can be confusing.  We take a moment here to reflect on a couple of the “odd” ones before we move on to the leg. You reviewed the hamstrings in the last lab.  But it may be worth reminding yourself that the hamstrings are depressor musculature (roughly corresponding to the biceps brachii muscle in the arm). They receive motor branches from the tibial portion of the sciatic nerve. The hamstrings can flex the knee and extend the hip joint. In this context, one might ask why the part of adductor magnus that does not cross the knee is innervated like a hamstring?  Despite the fact that it cannot act on the knee, the bundle of adductor magnus muscle fibers inserting into the adductor tubercle is developmentally part of the hamstring muscle group, and thus receives motor innervation from the tibial component of the sciatic nerve.

The innervation of the pectineus can also be confusing.   Although the pectineus muscle receives most of its innervation from the femoral nerve and is not far removed from the psoas major muscle in its course and attachments, its medial edge commonly receives some motor fibers from the obturator nerve. In some mammals, the femoral and obturator parts of the pectineus muscle are separate muscles. The human pectineus muscle may be a mosaic of functions; both the adductor and iliopsoas muscle components. Here we will treat pectineus as part of the adductor group, but it could just as easily be classified with the iliopsoas muscle.

The biceps femoris muscle raises interesting issues with innervation as well. As you remember from last lab, the short head of biceps femoris is not really a hamstring.  It might be best considered as an isolated elevator muscle that inserts with the long head of biceps femoris. The short head is therefore innervated by the posterior-division fibers from the fibular portion of the sciatic nerve.

 

5. EXTENSOR COMPARTMENT OF THE LEG: TIBIALIS ANTERIOR, EXTENSOR HALLUCIS LONGUS, EXTENSOR DIGITORUM LONGUS, FIBULARIS (PERONEUS) TERTIUS, LONGUS, AND BREVIS MUSCLES

The elevator musculature in the leg lies within the extensor compartment, which is subdivided into an anterior and a lateral (or fibular/peroneal) compartment.

  1. On the lateral side of the leg, find the posterior intermuscular septum of the leg (the lateral boundary between the elevators and depressors).
  2. Anterolaterally, locate the anterior intermuscular septum which divides the elevator compartment into anterior and lateral (fibular) compartments.

Posterior division motor fibers are carried from the sciatic nerve into the extensor (anterior and lateral) compartments of the leg as the common fibular [=peroneal] nerve.

 

  1. Find the common fibular [aka peroneal] nerve.
  2. Trace its path as it winds around the side of the fibular head between the attachment of the biceps femoris muscle and the origins of the ankle plantar flexors.
  3. Note where the common fibular nerve divides into deep and superficial branches.
  4. Trace the superficial fibular branch into the lateral compartment, and the deep fibular branch down into the anterior compartment.
 

 

  1. Find the tibialis anterior muscle arising from the anterior surface of the tibia.

The tibialis anterior muscle is found in the anterior component of the elevator compartment. It dorsiflexes the ankle and inverts the foot.

  1. Consult an articulated skeleton to locate its insertion into the base of the first metatarsal and the medial cuneiform.
  2. Open the deep fascia on the front of the leg and lift the tibialis anterior muscle to follow the deep fibular branch of the common fibular nerve.
  3. Lateral to the tibialis anterior muscle, separate out the extensor mass, which originates from the front of the fibula.

Both edges of this digital extensor mass are specialized. They have separate tendons and names of their own: the extensor hallucis longus muscle to the first digit and the fibularis tertius muscle to the fifth digit. The fibularis tertius is the only muscle which both everts and dorsiflexes the foot. The extensor digitorum longus muscle, located between these two specialized portions, also contributes a tendon to the 5th digit, along with tendons to digits 2, 3, and 4.

 

 

  1. Trace the anterior tibial artery down to the point at which it becomes the dorsalis pedis artery.
 

 

  1. Locate the lateral (fibular) compartment and distinguish the fibularis longus from fibularis brevis muscles. 

FUNCTIONAL ANATOMY:
The tibialis anterior and fibularis longus muscles form a sling or stirrup underneath the foot. This sling can be tightened to lend additional support to the arches as the heel leaves the ground during locomotion. The tibialis anterior muscle is also needed to hold the toes clear of the ground as the foot is brought forward during the swing phase of gait.

 

6. FLEXOR COMPARTMENT OF THE LEG: GASTROCNEMIUS, PLANTARIS, POPLITEUS, SOLEUS, FLEXOR HALLLUCIS LONGUS, FLEXOR DIGITORUM LONGUS AND TIBIALIS POSTERIOR MUSCLES

FUNCTIONAL ANATOMY:
The muscles in the flexor or posterior compartment of the leg comprise two sheet-like layers:

  1. A superficial layer that raises the heel (the two heads of the gastrocnemius, the soleus, and the plantaris muscles).
  2. A deeper layer containing a small muscle just behind the knee (the popliteus muscle) and three digital flexors that reach the sole by passing around the medial side of the heel (the flexor hallucis longus, flexor digitorum longus, and tibialis posterior muscles). 

At some point above the knee, the sciatic nerve ends by dividing into (1) its depressor (anterior-division) component, the tibial nerve, and (2) its elevator (posterior­ division) component, the common fibular nerve. The tibial nerve runs down the leg between the superficial sheet and deeper sheets of the flexor muscles, sending motor branches to the muscles in both layers.

 

  1. Within the popliteal fossa, locate the point at which the sciatic nerve divides into its two major branches: the tibial and common fibular.
  2. Trace the motor branches of the tibial nerve to the two heads of the gastrocnemius muscle.

 

  1. Separate the proximal part of the gastrocnemius muscle from the underlying soleus muscle.
  2. Transect the two heads of the gastrocnemius muscle a hand's breadth below their origins and reflect the muscle (black dotted line below).

Atlas Images:

 

  1. Note the bursa underlying the medial origin of the gastrocnemius muscle. 
  2. Locate the popliteus muscle running from the medial condyle of the tibia to the lateral femoral condyle as it crosses the knee joint.

The tendon calcaneus or Achilles' tendon is formed from the tendons of three muscles: 1) the gastrocnemius muscle, 2) the tiny plantaris muscle (both originating from the femur and thus crossing the knee joint), and 3) the soleus muscle (the largest of the three, arises from the tibia and fibula).

  1. Sever the calcaneal tendon, the plantaris tendon, and the tibial origin of the soleus muscle (blue dotted line in image above), and reflect the entire layer of plantar flexor muscles laterally.

The layer of deep fascia between the muscles that form the Achille’s tendon and the long digital flexors is called the intermuscular septum. The major vessels and nerves of the flexor (depressor) compartment plunge between the two heads of the soleus muscle to get into this layer of fascia, and run down the leg. As the femoral artery and vein pass into the leg, they change their names to the popliteal artery and vein.

 

 

  1. Between the two insertions of the adductor magnus muscle, follow the femoral artery and vein into the flexor compartment of the leg. Note that at this point, their names change to the popliteal artery and vein.
  2. Clean the vein and artery and define the gap through which they pass.

As the popliteal artery crosses the popliteus muscle, it gives off the anterior and posterior tibial arteries.

  1. Follow the popliteal artery into the leg and find its anterior and posterior tibial branches.
  2. Trace the anterior tibial artery into the extensor or anterior compartment.
  3. Trace the posterior tibial artery down the back of the leg and locate its fibular branch.

The fibular artery supplies the fibular side of the posterior compartment of the leg, but also sends branches to the lateral compartment.

  1. Continue following the posterior tibial artery around the medial side of the ankle into the foot.

Atlas Image:

 

 

Three muscles lie deep to the intermuscular septum in the leg. The digital flexors, like the deep layer of digital flexors in the forearm, comprise two parallel muscles: one to the great toe (or hallux) and one to the other four digits. Peculiarly enough, the two muscles originate on the "wrong" sides; the long flexor of the hallux (the flexor hallucis longus muscle) arises from the fibula, while the long digital flexor (the flexor digitorum longus muscle) arises from the tibia. The third muscle, the tibialis posterior muscle, divides into a fan of tendons inserting on the tarsal and metatarsal bones, and does not move any of the digits.

  1. On your cadaver, study the origins of the two digital flexors in the leg – the flexor digitorum longus and flexor hallucis longus muscles.
  2. Note that the flexor hallucis longus muscle arises partly from the fascia of the underlying tibialis posterior muscle.
  3. Free the medial edge of the flexor hallucis longus muscle enough to pull it laterally and see the origins of the tibialis posterior muscle.

Atlas Imges:

 

 

 

 

Lab 16 - The Foot

Suggested readings from
Gray's Anatomy for Students, 2nd ed.
Ch. 6: 600-627, 638-647

Suggested readings from Langman's Medical Embryology

11th ed: Ch 9 pp 134-42 -- Ch 10 pp 147-54
12th ed: Ch 11 pp 145-50 -- Ch 12 pp 151-61

 

Lab 16 Primary Lab Objectives:

  1. Remove the skin over the ankle and the foot. Identify and reflect the thick plantar aponeurosis on the sole of the foot.

  2. Locate the thenar and hypothenar muscles of the foot, consider the homologies of these muscles to those in the hand.

  3. Beginning in the leg, trace the tibial nerve and the posterior tibial artery. Trace the tibialis posterior, flexor digitorum longus, and flexor hallucis longus muscles into the foot. Consider the functional aspects of their pathways around the ankle. Identify the flexor hallucis brevis muscle.

  4. In the foot identify the quatratus plantae (flexor accessorius) and lumbrical muscles.

  5. Trace the lateral and medial plantar branches of the tibial nerve and posterior tibial artery onto the plantar surface of the foot. Trace the dorsalis pedis artery on the dorsal surface of the foot.

  6. Locate the adductor hallucis and interossei muscles and examine the deep muscles of the foot.

  7. Follow the muscles of the leg onto the lateral and medial aspects of the foot. Consider the relationship between these muscles as they pass into the foot and their role in foot movement.

  8. Sever the extensor retinaculum and examine the extensor musculature of the foot.

  9. Identify the fibularis longus and brevis muscles, noting the relationship between insertions of the fibularis longus and tibialis posterior muscles.

  10. Appreciate the origin and course of the tibialis posterior muscle, noting the complexity of its insertion.

 

Dissection Instructions

1. PLANTAR APONEUROSIS

  1. Remove the skin and superficial fascia from the ankle and foot, exposing the plantar aponeurosis.

NOTE: there is a thick fat pad beneath the heel that you will need to cut away to expose the plantar aponeurosis.

 

 

  1. Free the plantar aponeurosis along its distal edges, leaving it attached to the calcaneus
  2. Reflect the plantar aponeurosis, detaching it from the underlying muscles.
 

 

In the palm, removing the fascia covering the surfaced exposed the long flexor tendons. In the sole, removing the plantar aponeurosis exposes a layer of intrinsic musculature, arising from the calcaneus (and to some extent from the plantar aponeurosis itself): the flexor digitorum brevis muscle (shown below).

Atlas Images:

FUNCTIONAL ANATOMY:
The plantar aponeurosis acts as a tie-beam across the bottom of the longitudinal arches of the foot, helping to keep them from collapsing under pressure. Like the palmar aponeurosis, the plantar aponeurosis sends fascial extensions through to the deep transverse ligamentous structures that bind together the heads of the metatarsals. The long flexor tendon to each digit in the foot, therefore, moves through a fascial tunnel, and is surrounded by a synovial sheath (as in the hand). In humans, the first and second metatarsal heads are tied together by a deep transverse ligament. Unlike other primates, we cannot bring our big toe around into opposition the way we can our thumb.

 

 

2. THENAR AND HYPOTHENAR MUSCLES

  1. Find the abductor hallucis and abductor digiti minimi muscles. These muscles originate from the calcaneus on either side of the flexor digitorum brevis muscle.

Atlas Images:

FUNCTIONAL ANATOMY:
The abductor hallucis and abductor digiti minimi muscles are equivalents of the thenar and hypothenar abductors in the hand and have similar insertions. They have little power to abduct the digits in the foot, but are of considerable importance in relieving the strain in the plantar aponeurosis when we rise up on our toes.

The long digital flexor tendons pass into the sole between the abductor hallucis muscle and the underlying flexor hallucis brevis muscle. At the ankle, the intramuscular septum covering the digital flexors becomes ligamentous and forms a flexor retinaculum. This band of deep fascia restrains the flexor tendons as they pass behind the medial malleolus of the tibia.

 

 

3. SUPERFICIAL MUSCLES OF THE SOLE

  1. Sever the flexor retinaculum and transect the abductor hallucis muscle.
 
  1. Reflect these structures and trace the tibial nerve, and the posterior tibial artery.
  2. Trace the three tendons belonging to the tibialis posterior, flexor digitorum longus, and flexor hallucis longus muscles around the ankle and into the sole. 
  3. Note that the flexor hallucis longus muscle runs in a compartment of its own, which grooves the tibia and talus.
  4. Examine these grooves on a skeleton.
  5. Identify the underlying flexor hallucis brevis muscle.

NOTE: Use your blunt probe to define these muscles and gently separate the nerves and vessels from the surrounding fascia. In the sole, the tendon of the flexor hallucis longus muscle runs straight to the distal phalanx of the hallux, while the tendon of the flexor digitorum longus muscle crosses it at an angle.

Atlas Images:

 

 

 

4. QUADRATUS PLANTAE (FLEXOR ACCESSORIUS)

  1. Locate where the flexor hallucis longus and the flexor digitorum longus muscles cross in the foot.
  2. Identify and define the borders of the quadratus plantae and the lumbrical muscles.

NOTE: the lumbricals are tiny muscles that take their origin from the tendon of the flexor digitorum longus.

 

FUNCTIONAL ANATOMY
In order to resolve the oblique pull on the flexor digitorum longus tendon, a little sheet of muscle, the quadratus plantae (or flexor accessorius), arises from the calcaneus and inserts into the posterior edge of the long flexor tendon. The lumbricals originate from the digital tendons (as in the hand) and pass over (plantar to) the deep transverse metatarsal ligaments to the extensor expansions.

 

 

5. TIBIAL NERVE AND POSTERIOR TIBIAL ARTERY

The tibial nerve divides into the lateral and medial plantar branches (respectively equivalent to the ulnar and median nerves in the palm) as it passes under the flexor accessorius.

  1. Locate the tibial nerve in the flexor compartment of the leg and follow it to the quadratus plantae (flexor accessorius).
  2. Determine where it splits into the medial and the lateral plantar branches.

Atlas Images:

FUNCTIONAL ANATOMY:
Like the median nerve, the medial plantar nerve sends motor branches to the "thenar" muscles of the first digit, and superficial sensory branches to the first 3 1/2 digits. The median nerve innervates the flexor digitorum superficialis muscle in the forearm; likewise, the medial plantar nerve innervates the equivalent flexor digitorum brevis muscle in the sole of the foot.

 

  1. Follow the medial plantar branch of the tibial nerve into the foot.
  2. Trace offshoots of this nerve into the flexor hallucis brevis and flexor digitorum brevis muscles.

Like the ulnar nerve, the lateral plantar nerve spreads across the sole deep to the long flexor tendons, innervating the deeper intrinsic muscles.

  1. Follow the lateral plantar branch into the foot and locate its muscular branches to the abductor digiti minimi muscle (at this point, you cannot see its branches to the interossei or other deep muscles).
 

 

  1. Trace the posterior tibial artery into the foot.

The posterior tibial artery also divides into the lateral and medial plantar branches.  The lateral plantar artery is equivalent to the ulnar artery and has corresponding deep and superficial branches. The medial plantar artery is not entirely equivalent to the radial artery, only to its superficial branch. The deep branch of the radial artery is represented in the foot by the artery of the extensor compartment (the anterior tibial artery).

  1. Locate its medial and lateral plantar branches accompanying the nerves of the same names.
  2. Trace the anterior tibial artery onto the dorsum of the foot where it becomes the dorsalis pedis artery.
  3. Follow the dorsalis pedis artery to the point where it disappears between the two heads of the first dorsal interosseous muscle.

Atlas Images:

 

 

6. DEEP MUSCLES OF THE SOLE

  1. Sever the tendon of the flexor digitorum longus muscle where it crosses the flexor hallucis longus tendon.
  2. Transect the belly of the quadratus plantae.
  3. Confirm that a few fibers of the flexor hallucis longus muscle go to the flexor digitorum longus tendon; a vestige of the primitive union of the two tendons.
  4. Cut this connection.
 

 

  1. Reflect the flexor digitorum longus muscle distally with the attached short muscles (lumbricals and quadratus plantae)
  2. Expose and identify the deep intrinsic muscles of the foot: the interossei and the adductor hallucis muscles. 
  3. Trace the tendon of the flexor hallucis longus muscle out to its insertion
  4. Cut the tendon proximal to the insertion, and reflect it toward the heel. This exposes the deeper layer of "thenar" muscles more completely.

 

 

7. FLEXOR HALLUCIS LONGUS AND BREVIS

FUNCTIONAL ANATOMY:
The insertions of the abductors (the flexor hallucis brevis muscle and the flexor brevis muscle of the fifth toe) are equivalent to the hand muscles except that the flexor hallucis brevis muscle attaches to both sesamoids of the big toe.  These sesamoids, rather than the head of the first metatarsal itself, bear the weight transmitted through the ball of the foot. They are needed to ensure that no weight falls on the tendon of the flexor hallucis longus muscle, which passes between the sesamoid bones.

  1. Trace the flexor hallucis brevis muscle to the sesamoids.
  2. Locate the tendon of the flexor hallucis longus muscle passing between the sesamoids.
  3. Reassemble the sole of the foot, and compare it with the palm of the hand.
 

 

 

8. EXTENSORS OF THE FOOT

FUNCTIONAL ANATOMY:
The deep fascia on the dorsal surface of the foot is condensed to form the extensor retinacula. The extensor retinacula holds down the tendons of the elevator muscles.  In the leg, the fibularis longus and brevis muscles are enclosed in their own separate compartment and have their own fibular retinaculum above and below the ankle.

Atlas Images:

 

  1. Sever the extensor retinacula and trace the tendons of the extensor digitorum longus and extensor hallucis longus muscles down to their respective insertions.
  2. Dissect out the extensor expansion on the second digit.
  3. Compare the second digit of the foot with the second digit of the hand.
  4. Transect and reflect the extensor digitorum longus muscle to see the underlying extensor digitorum brevis muscle.
  5. Underneath and distal to the extensor digitorum brevis muscle identify the dorsal interosseus muscles.

The extensor digitorum brevis muscle arises from the calcaneus and inserts into the extensor expansions of digits II-IV. The tendon passing to the first digit is distinguished by a separate name: the extensor hallucis brevis muscle. The hallucal attachment differs from the other digits resembling that of the extensor pollicis brevis in the hand.

Atlas Images:

 

 

9. FIBULAR COMPARTMENT

  1. Open the fibular compartment.
  2. Sever any remaining fibers of the extensor retinaculum.
  3. Trace the fibularis brevis muscle to its insertion.
  4. Also examine the small fibularis tertius muscle, a small muscles found primarily in humans, and trace it to its insertion. Note that this muscles follows a different path from the other muscles that bear the name fibualri.

The fibularis longus and tibialis anterior muscles (both elevators) form a sling or stirrup underneath the foot, which may help to support the arch when they contract.

  1. Expose the sole of the foot.
  2. Locate the insertions of the fibularis longus and tibialis anterior muscles.
 

 

 

10. TIBIALIS POSTERIOR MUSCLE

FUNCTIONAL ANATOMY:
The tibialis posterior muscle was not examined previously because its insertion lies deep to all the other structures of the sole. Like the flexor hallucis longus muscle, the tibialis posterior muscle occupies a groove in the distal end of the tibia just behind the ankle. The tibialis posterior is a specialized flexor muscle whose tendon spreads out to insert into the tarsal bones (except the talus) and at least the middle three metatarsals. Some of its fibers pass into the flexor hallucis brevis muscle, so it has a secondary attachment to the pollex  as well. It aids the deeper ligaments of the foot in sustaining the medial arch and in preventing the head of the talus from being pushed downward between the calcaneus and the navicular.

  1. Trace the tibialis posterior muscle behind the ankle around to its complex insertion.
 

 

 

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