Back to “Memory Booster of Regional Anatomy”


8. Lower limb



< Cutaneous veins >


Fig. 8-1.BMP

Fig. 8-1. Great and small saphenous veins.


Cutaneous veins in the lower limb start with the dorsal venous arch of foot which corresponds to the dorsal venous network of hand (Fig. 2-22). From the arch, the great and small saphenous veins ascend.



We do not use the terms “greater and lesser” but “great and small” for saphenous veins and cardiac veins (Fig. 5-26). A general rule is that the terms “greater and lesser” are only applied when structures are relatively similar. Such examples are the tubercles in humerus (Fig. 2-18) and the curvatures in stomach (Fig. 6-31). However, this rule is not strict.

While the great saphenous vein passes anterior to the medial malleolus, the small saphenous vein passes posterior to the lateral malleolus (Fig. 8-1). Eventually, the great saphenous vein on the front reaches the femoral vein (which is great) on the front (Fig. 8-3), whereas the small saphenous vein on the back reaches the popliteal vein (which is small) on the back (Fig. 8-25).



Unlike the saphenous vein, a deep vein goes along with a deep artery; for instance, the femoral vein travels with the femoral artery (Fig. 8-10). Blood in the saphenous vein flows to the deep vein through the perforating vein; this is a kind of anastomosis. In fact, the perforating vein perforates muscles.

Venous valves with two cusps are located in the saphenous and perforating veins. When venous valves are damaged, blood accumulates in the saphenous vein; this is a disease called varicose vein.

The cutaneous vein, perforating vein, and venous valve are found not only in the lower limb but also in the upper limb (Fig. 2-22). However, there is no varicose vein in the upper limb because it is easy for blood to flow from the upper limb to the heart due to their comparable altitude.

< Thigh >


Fig. 8-2. Thigh muscles.


Thigh muscles are covered by the fascia lata, which is homologous to the brachial fascia for arm muscles (Fig. 2-24). The lateral part of the fascia lata is thickened to become the iliotibial tract (Fig. 8-14). Commonly, the term “tract” is used for specifying the collected axons (Fig. 2-10) in the brain and spinal cord.


Fig. 8-3. Emptying of great saphenous vein.


The fascia lata has the saphenous opening where the great saphenous vein passes to empty into the femoral vein (Fig. 8-1). The superficial inguinal nodes exist in front of the saphenous opening. The superficial inguinal nodes are superficial enough to be palpable when they are enlarged (Fig. 7-22).

In Fig. 8-2, three intermuscular septa result in anterior, medial, and posterior thigh muscles that are innervated by the femoral, obturator, and sciatic nerves (Fig. 7-15), respectively. Gluteal muscles controlled by the superior and inferior gluteal nerves lie superior to the posterior thigh muscles (Fig. 8-18).

Anterior thigh muscles include the iliopsoas that flexes the femur. Among the iliopsoas, the psoas major originates from the lumbar vertebrae, and is also a member of the posterior abdominal wall muscles (Fig. 6-54).


Fig. 8-4.BMP

Fig. 8-4. Sartorius.


Sartorius, the longest muscle in human body, arises from the anterior superior iliac spine. Interestingly, it descends anterior to the hip joint and posterior to the knee joint; therefore, it flexes both joints (Fig. 8-15). A sartor (tailor) usually contracts this muscle to cross his/her legs when sewing, which is the etymology of the muscle name.


Fig. 8-5.BMP

Fig. 8-5. Quadriceps femoris.


The quadriceps femoris corresponds to the triceps brachii in upper limb (Fig. 8-24), except the fact that the quadriceps femoris has one more head. The rectus femoris passes two joints as the long head of triceps brachii passes two joints (Fig. 2-28). The quadriceps femoris moves two joints when kicking a ball. Of course, its main action is the knee extension (Fig. 8-15).

The rectus femoris is relatively deeper than the sartorius, so the origin of rectus femoris (anterior inferior iliac spine) is lower than that of the sartorius (anterior superior iliac spine) (Fig. 8-4). The vastus intermedius originating from the femur is covered by the rectus femoris. This spatial relationship is like that the medial head of triceps brachii is concealed by the long head (Fig. 2-28). The vastus lateralis and medialis originate from the lateral and medial lips of linea aspera, respectively (Fig. 8-22).

The common tendon of the quadriceps femoris has the biggest sesamoid bone (Fig. 2-36) called patella. Without the patella, the tendon would easily be worn out by the friction with underlying femur (Fig. 2-37). Both the patella and femur have corresponding articular surfaces covered by articular cartilage (Fig. 2-59).

The tendon distal to the patella is named patellar ligament, which is attached to the tibial tuberosity. The patellar “ligament” is a proper term as it connects two bones (patella and tibia) (Fig. 2-58).



When the patellar ligament is tapped just below the patella, the quadriceps femoris is lengthened. By the reflex, the quadriceps femoris is involuntarily contracted to make the leg kick.



When you kneel, the tibial tuberosity does hit the floor.


Fig. 8-6.BMP

Fig. 8-6. Pectineus.


The last anterior thigh muscle is the pectineus. The name “pectineus” comes from the “pecten” pubis (a part of pelvic brim) which is the origin of this muscle (Fig. 7-2).

Three anatomical terms have an identical meaning, a comb: the pectinate muscles in the atrium (Fig. 5-15), the pectinate line in the anal canal (Fig. 7-39), and the pecten pubis. However, only the pectinate muscles physically resemble a comb.

The pectineus, innervated by both the femoral and obturator nerves (Fig. 8-2), has two actions (flexion and adduction of femur).


Fig. 8-7.BMP

Fig. 8-7. Gracilis.


Among the medial thigh muscles, only gracilis passes two joints. However, gracilis performs the same action as other medial thigh muscles (adduction of the hip joint) since the knee joint is a hinge joint with collateral ligaments (Fig. 8-46) and thus cannot be adducted. The gracilis is a gracile (gracefully thin) muscle.


Fig. 8-8. Adductor muscles, obturator externus.


Adductor longus, brevis, and magnus are arranged from anterior to posterior. These German-like terms’ order can be remembered by a word, ALBuM (Adductor Longus, Brevis, und Magnus). The adductor longus and brevis originate from the pubis, but the adductor magnus originates from the ischium. This is so because the ischium is located posterior to the pubis (Figs. 7-4,5).

The insertion of these three adductors is the medial lip of linea aspera. Following its name, the adductor magnus has a large insertion, where the adductor hiatus exists (Fig. 8-10). It is like the esophageal hiatus and aortic hiatus that are found in the diaphragm (Fig. 5-47).

The origins of three adductors are closer to the hip joint than their insertion, since the hip adduction does not need to be performed in a big angle.



Those medial thigh muscles are to prevent a rider from falling off a horse.



Some borderline muscles have dual innervation. The pectineus (Fig. 8-6) is innervated by the femoral and obturator nerves. The adductor magnus (Fig. 8-8) is innervated by the obturator and sciatic nerves (Fig. 8-2).

The obturator externus is a supplementary medial thigh muscle. This muscle is from the external surface of the obturator membrane to the vicinity of the greater trochanter. Its action is not only to adduct but also to laterally rotate the femur (Figs. 7-7, 8-8).


Fig. 8-9. Femoral triangle.


Now we are ready to talk about the femoral triangle with three boundaries: the medial border of sartorius, medial border of adductor longus, and inguinal ligament. The femoral triangle which is deep does not include the superficial sartorius (Fig. 8-4) but the deep adductor longus (Fig. 8-8). The femoral triangle also contains the pectineus (Fig. 8-6) and iliopsoas (Fig. 6-54) which are deep as well.



A tip to memorize the three boundaries is the word SAIL (Sartorius, Adductor longus, and Inguinal Ligament).



In the femoral triangle, sequential location of the femoral nerve, artery, and vein is memorable with NAVY. It is interesting that the NAVY is related with the SAIL (femoral triangle). The intervening femoral artery’s pulse is readily palpable in a living person, so we can imagine the location of the nearby femoral nerve and vein.


Fig. 8-10.BMP

Fig. 8-10. Femoral artery and vein.


The femoral vein is single, unlike the brachial veins which are accompanying veins (Fig. 2-23).

The femoral artery and vein are enclosed by femoral sheath, while the femoral nerve is not (Fig. 8-3). It is unusual that a sheath does not contain nerve; for a usual example, the carotid sheath covers the nerve, artery, and vein (Fig. 3-32). Instead, the femoral sheath surrounds the deep inguinal node (Figs. 7-22, 8-3) which is located in the femoral canal.

Most lymph in the lower limb drains to the deep inguinal node which is around the end of the femoral vein. The rest of the lymph enters the superficial inguinal node which is around the end of the great saphenous vein (Fig. 8-3). Lymph in two inguinal nodes ascends to the external iliac node (Fig. 7-22).

The femoral sheath is known to be a structure extended from the transversalis fascia above the inguinal ligament (Figs. 6-5,6).


Fig. 8-11.BMP

Fig. 8-11. Femoral ring, adjacent structures.


In the figure above, the plane is almost horizontal to pass both the inguinal ligament (Fig. 6-7) and pecten pubis (Fig. 7-2). The plane shows three structures in the femoral sheath: the border between external iliac and femoral arteries (Fig. 8-12), the border between corresponding veins, and the femoral ring which is superior opening of femoral canal (Fig. 8-10).

As a pathologic condition, the small intestine can pass through the femoral ring to enter femoral canal (femoral hernia). Like this, the femoral canal is related to the digestive tract. It is because the femORAL cANAL includes ORAL and ANAL. Do not be serious.

Just as the femoral ring is the superior opening of the femoral canal, the adductor hiatus (Fig. 8-8) is the inferior opening of the adductor canal. Unlike the femoral canal which includes the deep inguinal node, the adductor canal includes the femoral artery and vein (Fig. 8-10).



After passing through the adductor hiatus, the femoral artery and vein become the popliteal artery and vein. The femoral artery is lateral to the femoral vein while the popliteal artery is medial to the popliteal vein (Fig. 8-24). This indicates that the femoral artery crosses the femoral vein (Fig. 8-10).


Fig. 8-12.BMP

Fig. 8-12. Femoral artery.


Notable branches of the femoral artery are the superficial circumflex iliac artery and the external pudendal artery. The two correspond to the deep circumflex iliac artery from the external iliac artery (Fig. 7-19) and the internal pudendal artery from the internal iliac artery (Fig. 7-20), respectively.

As the brachial artery has the deep brachial artery (Fig. 2-62), the femoral artery has the deep femoral artery. Between the femoral and deep femoral arteries, adductor longus intervenes (Fig. 8-8). Consequently, the femoral artery accompanies the femoral nerve (Fig. 8-11) which innervates the anterior thigh muscles; the deep femoral artery runs along the obturator nerve which is responsible for the medial thigh muscles (Fig. 8-2).

Unlike the anterior and posterior circumflex humeral arteries that originate from the axillary artery (Fig. 2-17), the medial and lateral circumflex femoral arteries originate from the deep femoral artery.



The gluteal surface of the ilium has three gluteal lines which are the borders between the three gluteus muscles’ origins (Figs. 8-13,16). There is not enough space inferior to the inferior gluteal line for an additional muscle.


Fig. 8-13. Gluteus maximus.


The gluteus maximus originates from the sacrum, the sacrotuberous ligament, and the area posterior to the posterior gluteal line.



Due to the vast origin, the gluteus maximus covers most of the gluteal region (buttock), including the ischial tuberosity; however, it does not in the seated posture. Thus, when sitting, the ischial tuberosity (Fig. 7-5) touches the chair without the cover by the gluteus maximus.



The deltoid muscle in the upper limb and the gluteus maximus are equivalent. The two big muscles have similar insertions: the deltoid tuberosity (Fig. 2-1) and the gluteal tuberosity. The gluteal tuberosity is an extended structure of the lateral lip of linea aspera (Fig. 8-22). Another insertion of the gluteus maximus is the iliotibial tract (Figs. 8-13,14).

Let us think about the action of the gluteus maximus. Three axes of the hip joint pass the center of head of femur (Figs. 2-3, 8-45). Regarding the mediolateral axis of hip joint, its action is extension (Fig. 8-15); regarding the superoinferior axis, its action is lateral rotation. Regarding the anteroposterior axis, it has no actions since the muscle passes the axis (Fig. 8-13).


Fig. 8-14.BMP

Fig. 8-14. Iliotibial tract.


The “iliotibial” tract, which is the thickened portion of the fascia lata (Fig. 8-2), connects the “iliac” tubercle (on the iliac crest) with the lateral condyle of “tibia” (Fig. 8-46). The two bone structures can be palpated in one’s body; so the iliotibial tract is a superficial structure.

The iliotibial tract plays the role of an aponeurosis for the gluteus maximus (for extension of hip joint) (Fig. 8-15) and the tensor fasciae latae (for flexion of hip joint). The iliotibial tract passes the mediolateral axis of the knee joint, so it does not affect knee movement.

Even though the tensor fasciae latae flexes the hip joint, the muscle belongs to gluteal muscles since it is innervated by the superior gluteal nerve (Fig. 8-18). As the name shows, the “tensor fasciae latae” additionally “tenses fascia lata” by the way of the iliotibial tract (Fig. 8-2).



In the lower limb, extensor muscles are more developed.


Fig. 8-15.BMP

Fig. 8-15. Extension of lower limb.


Representative extensor muscles in the lower limb are the gluteus maximus (hip joint) (Fig. 8-13) and quadriceps femoris (knee joint) (Fig. 8-5). If two joints are extended, they allow us to get up and jump.


Fig. 8-16. Gluteus medius and minimus.


The gluteus medius and gluteus minimus, heading to the greater trochanter, descend laterally to the anteroposterior axis of hip joint, so they abduct the femur.



When one stands on one’s right foot, the right gluteus medius and minimus pull down the right side of the pelvic skeleton for balance. Origin and insertion are switched (Fig. 8-16).


Fig. 8-17. Deep gluteal muscles.


In the gluteal region, we can see that the piriformis comes out through the greater sciatic foramen and the obturator internus comes out through the lesser sciatic foramen. Note that the border of two muscles is the ischial spine (Figs. 7-5,6). As previously mentioned in pelvis, perineum chapter, they rotate the femur laterally (Fig. 7-7).

The obturator internus is assisted by twin muscles, the superior gemellus from the ischial spine and the inferior gemellus from the ischial tuberosity. The twin muscles terminate at the tendon of obturator internus. Readers will see another muscle terminating at the tendon, quadratus plantae (Fig. 8-40).

The last muscle is the quadratus femoris that originates from the ischial tuberosity and inserts at the intertrochanteric crest. Considering the two axes of the hip joint, the quadratus femoris rotates the femur laterally and adducts the femur.

We can simply say that the main action of all deep gluteal muscles is the lateral rotation of the femur.

The greater trochanter is greater than the lesser trochanter because it has more muscles attached to it (Figs. 7-7, 8-16,17); the greater tubercle of humerus is greater for the same reason (Figs. 2-2,18).



The greater trochanter is the landmark for measuring the hip circumference.


Fig. 8-32.BMP

Fig. 8-18. Gluteal muscles and nerves.


The gluteus maximus is innervated only by the inferior gluteal nerve (Fig. 7-15). This may be because the superior gluteal nerve is already occupied innervating the superior three muscles (gluteus medius, gluteus minimus, and tensor fasciae latae). The gluteus maximus differs from the pectoralis major which is innervated by two nerves (Fig. 2-20). The gluteus maximus is close to the deltoid muscle (Fig. 2-1) innervated by one (axillary) nerve (Fig. 2-15).

The remaining deep gluteal muscles (Fig. 8-17) are governed by anonymous short nerves of the sacral plexus (Fig. 7-15). Read the comics on the anonymous nerves below Fig. 7-12.


Fig. 8-33.BMP

Fig. 8-19. Course of sciatic nerve (After reflecting gluteus maximus).


The sciatic nerve penetrates the greater sciatic foramen just beneath the piriformis (Fig. 7-15), then descends posterior to the obturator internus and quadratus femoris (Fig. 8-18).


Fig. 8-20. Course of sciatic nerve.


The sciatic nerve passes the midpoint of the ischial tuberosity and the greater trochanter. In order not to injure the sciatic nerve, intramuscular injection to the gluteus maximus is conducted on the superior lateral quadrant of the gluteal region.


Fig. 8-21. Semitendinosus, semimembranosus.


Let us now discuss the posterior thigh muscles (hamstring muscles) (Fig. 8-2). In etymology, the SEMITENDinosus has a distal TENDon which is HALF the length of the muscle, and SEMIMEMBRANosus is relatively thin LIKE a MEMBRANe.

Two muscles share a common origin (ischial tuberosity). However, the insertion of the superficial semitendinosus is lower than that (medial condyle of tibia) of the deep semimembranosus. Take notice that the sartorius (Fig. 8-4), gracilis (Fig. 8-7), and semitendinosus all share the common insertion in the tibia.


Fig. 8-22.BMP

Fig. 8-22. Biceps femoris.


The biceps femoris is homologous to the biceps brachii (Fig. 8-24). However, the short head of the biceps femoris passes only one joint unlike the short head of the biceps brachii which passes two joints (Fig. 2-25). The short head of the biceps femoris is fully covered by the long head.

Since the posterior thigh muscles pass hip and knee joints, the muscles extend the hip and flex the knee (Fig. 8-15). The main action, nonetheless, is the knee flexion. Regard the muscles as the antagonists of the quadriceps femoris (Fig. 8-5). Football players frequently make a sudden knee extension which can strain a tendon of the posterior thigh muscles.

< Popliteal fossa >


Fig. 8-23.BMP

Fig. 8-23. Popliteal fossa.


Two superior borders of the popliteal fossa are the posterior thigh muscles (Figs. 8-21,22), while its two inferior borders are the gastrocnemius (Fig. 8-35).



While the cubital fossa is triangular (Fig. 2-29), the popliteal fossa is quadrangular.


Fig. 8-24.BMP

Fig. 8-24. Development of upper and lower limbs.


Why is the cubital fossa on the anterior side, while the popliteal fossa is on the posterior side? When the limbs develop, the dorsa of both hand and foot initially face lateral. After birth, the shoulder and hip joints are extended (Figs. 2-31, 8-15) to stand up, while the dorsa still face lateral.

To shift into the anatomical position, the upper and lower limbs are rotated laterally and medially at 90 degrees, respectively. Accordingly, if we stand on tiptoe, the dorsa of the hand and foot face posterior and anterior, respectively. This is why the cubital and popliteal fossae are on reverse sides.

For the same reason, homologous structures in the upper and lower limbs are on the different sides. For instance, the biceps brachii is an anterior arm muscle (Fig. 2-25), the biceps femoris is a posterior thigh muscle (Fig. 8-22).


Fig. 8-25.BMP

Fig. 8-25. Structures of popliteal fossa.


The popliteal fossa includes the popliteal artery, popliteal vein (Fig. 8-10), tibial nerve, and common fibular nerve (Fig. 8-19). The small saphenous vein enters the popliteal vein (Fig. 8-1).


Fig. 8-26.BMP

Fig. 8-26. Division of popliteal artery.


After removing the gastrocnemius and soleus (Fig. 8-35), one can see that the popliteal artery divides into the anterior and posterior tibial arteries just below the popliteus which is a posterior leg muscle (Fig. 8-38).

The anterior tibial artery passes the interosseous membrane to feed the anterior leg muscles. The posterior tibial artery feeds posterior leg muscles. Fibular artery, a branch of the posterior tibial artery, feeds the lateral leg muscles (Fig. 8-27).

< Leg >


Fig. 8-27.BMP

Fig. 8-27. Leg muscles.


The medial surface of the tibia is not covered by muscles. Even in an obese person, the medial surface is palpable over the skin and minimal subcutaneous tissue; it is vulnerable to mechanical impact.

Like the ulna and radius, the tibia and fibula are connected by the interosseous membrane (syndesmosis) (Fig. 2-32). However, unlike the forearm, the leg cannot perform pronation and supination. It is because while the proximal ends of ulna and radius form the mobile pivot joints, those of tibia and fibula do not (Fig. 8-46).

Besides the two bones and one interosseous membrane, two intermuscular septa partition the leg muscles, all of which are encircled by the crural fascia.

The schematic drawing above indicates that the anterior, lateral, and posterior leg muscles are innervated by the deep fibular, superficial fibular, and tibial nerves, respectively. In fact, the sciatic nerve bifurcates at the posterior thigh (Fig. 8-19); the common fibular nerve bifurcates at the neck of fibula (Fig. 8-46). The pattern of the nerve division differs from that of the artery division (Fig. 8-26).



How is the dual mnemonics of the crural fascia?


Fig. 8-28.BMP

Fig. 8-28. Three retinacula of ankle.


Whereas the wrist has two retinacula (Fig. 2-52), the ankle has three: the extensor, fibular, and flexor retinacula for tendons of the anterior, lateral, and posterior leg muscles. Like in the wrist, the tendons in the ankle are surrounded by synovial sheaths.



We do not use the terms, “extension” and “flexion” of the ankle joint (Fig. 8-15). Instead, we use the terms, “dorsiflexion (moving toward the dorsum of foot)” and “plantar flexion (moving toward the sole).”



While dorsiflexion and plantar flexion are the movements above the talus, inversion and eversion are the movements below the talus. In fact, the axis of the former movement is a line connecting medial and lateral malleoli, while the axis of the latter movement passes the 2nd metatarsal bone (Fig. 8-33).


Fig. 8-29. Tibialis anterior.


Frequently, the foot is 90 degrees plantar flexed (tiptoe like a ballerino/ballerina) (Fig. 8-24), in order to represent the leg muscles efficiently. These drawings are also helpful for comparing the leg muscles with the forearm muscles (Fig. 2-34).

Be remindful of the insertion of each muscle, as the insertion greatly influences the action of the muscle. The tibialis anterior goes to the 1st metatarsal bone to result in the dorsiflexion and inversion (Fig. 8-33).

While the 1st carpometacarpal (saddle) joint is very mobile (Fig. 2-56), the 1st tarsometatarsal joint is not. Therefore, whereas the muscles affecting the wrist joint do not end at the 1st metacarpal bone but at the 2nd metacarpal bone (Fig. 2-47), the muscles operating the ankle joint end at the 1st metatarsal bone (Figs. 8-29,32,33).


Fig. 8-30. Long extensors (Left) and short extensors (Right) of toes.


Extrinsic and intrinsic muscles of the dorsum of foot are shown on a single figure due to the same action and the same innervation by the deep fibular nerve (Figs. 8-27,37).

The extensor hallucis longus ends at the 1st distal phalanx, while the extensor hallucis brevis ends at the 1st proximal phalanx. Their insertions are identical to that of the extensor pollicis longus (1st distal phalanx) and that of the extensor pollicis brevis (1st proximal phalanx) (Fig. 2-49).

The extensor digitorum longus and brevis fuse to become the extensor expansion. However, in the upper limb, extensor digitorum forms the extensor expansion with some contribution of the extensor digiti minimi and extensor indicis (Figs. 2-44,51).


Fig. 8-50.BMP

Fig. 8-31. Fibularis tertius.


Unlike the two other fibularis muscles which are soon to be introduced (Fig. 8-32), the fibularis tertius belongs to the anterior leg muscles. As anticipated, it is because the muscle is controlled by the deep fibular nerve (Fig. 8-27). Moreover, its action is dorsiflexion like other anterior leg muscles. An additional action of this laterally located muscle is eversion (Fig. 8-33).


Fig. 8-32. Fibularis longus and brevis.


Lateral leg muscles consist of two muscles (Fig. 8-27). The fibularis brevis ends at the 5th metatarsal bone like the fibularis tertius (Fig. 8-31). Difference is that the fibularis brevis and tertius pass posterior and anterior to the lateral malleolus, in that order (Fig. 8-33).

The fibularis longus has a higher origin than the fibularis brevis. Under the fibular retinaculum (Fig. 8-28), the tendon of the fibularis longus is posterior to that of the fibularis brevis and traverses the sole (Fig. 8-33). It can be said that the longus takes a long route indeed.


Fig. 8-33. Five muscles moving ankle joint (Coronal plane).


This schematic figure demonstrates the courses of the five muscles that end at the metatarsal bones. They are equivalent to the five muscles that end at the metacarpal bones (Fig. 2-47). Note that the foot is not plantar flexed in the above figure (anatomical position).

With regard to the axis of the medial and lateral malleoli, the anterior leg muscles (tibialis anterior, fibularis tertius) (Figs. 8-29,31) induce dorsiflexion while the lateral leg muscles (fibularis longus and brevis) (Fig. 8-32) and posterior leg muscle (tibialis posterior) (Fig. 8-36) induce plantar flexion. Considering the axis of the 2nd metatarsal bone, the tibialis muscles make inversion, whereas the fibularis muscles contribute to eversion.



The five muscles are regrouped in the comic strip. Even though the fibularis family outnumbers the tibialis family, the tibialis muscles are stronger; think of the tibia which is more robust than the fibula (Figs. 8-27, 46). Therefore, the power of inversion is dominant. When one loses one’s footing, an inversion sprain is more frequent than an eversion sprain.


Fig. 8-34. Difference of transverse and horizontal planes.


The transverse (cross) plane of leg is a horizontal plane (Fig. 8-27), while the transverse plane of foot is a coronal plane (Fig. 8-33). Thus we can remind ourselves that a transverse plane does not equal a horizontal plane.


Fig. 8-35.BMP

Fig. 8-35. Superficial posterior leg muscles.


Three superficial posterior leg muscles (gastrocnemius (Fig. 8-23), plantaris, and soleus) have a common insertion tendon which is the calcaneal tendon attached to the calcaneus. Their common action is plantar flexion.



When this calcaneal (Achilles) tendon is injured, one is unable to raise one’s heel. Hence Achilles tendon is figuratively used for vulnerable point.

Expectedly, the superficial gastrocnemius (origin: medial and lateral condyles of femur) is longer than the deep soleus (main tibial origin: soleal line). However, it comes as a surprise that the intermediate plantaris (origin: lateral supracondylar line) is the longest, so the plantaris going to the origin penetrates the gastrocnemius from underneath. The plantaris is visible in the popliteal fossa (Figs. 8-23,35).

GPS does not only stand for car navigation (Global Positioning System) but also for the three muscles (Gastrocnemius, Plantaris, Soleus). The three muscles are for car acceleration by stepping on a gas pedal. Their individual names have noteworthy meanings as follows.

The gastrocnemius, combination of gastro (belly) and cnemius (leg), can be interpreted as a big muscle “belly” in “leg.”

Unlike the palmaris longus that reaches the palmar aponeurosis (Fig. 2-35), the plantaris does not reach the plantar aponeurosis (Figs. 8-35,39). The rationale for the term “plantaris” is its action which is “plantar” flexion.



The soleus, which is not a muscle in the sole (foot), is named after its shape resembling a fish sole. Its name results in its origin’s name, the soleal line (Fig. 8-35).


Fig. 8-36. Deep posterior leg muscles.


Underneath the three muscles, there are three deep posterior leg muscles that correspond to the anterior leg muscles. The tibialis posterior has been already introduced when describing the ankle joint movement (Fig. 8-33). The flexor digitorum longus and flexor hallucis longus match the extensor digitorum longus and extensor hallucis longus (Fig. 8-30).


Fig. 8-37.BMP

Fig. 8-37. Muscles, arteries, nerves under extensor and flexor retinacula.


Muscles, arteries, and nerves beneath the extensor retinaculum and flexor retinaculum are assigned single letters. In the right extensor retinaculum, DANH-T exists from fibula to tibia. In the right flexor retinaculum, T-DANH exists from the tibia to calcaneus (Fig. 8-28).

The tibialis anterior and posterior (two Ts) are both located immediately next to the tibia. Then the remaining DANH can be memorized with “Dick And Nervous Harry.” (In the old film “Dirty Harry,” Harry looked nervous.)

Distal to the flexor retinaculum, the flexor Hallucis longus (H) crosses the flexor Digitorum longus (D) to reach the great toe (Fig. 8-36). H crosses deep to D; as a result, H arrives at the 3rd layer of sole (Fig. 8-41), D arrives at the 2nd layer (Fig. 8-40). (Perhaps, the nervous Harry wants to get into the deeper place.)


Fig. 8-38.BMP

Fig. 8-38. Popliteus.


The deepest short muscle, the popliteus (Fig. 8-26), has the action of flexion and medial rotation of the knee joint. Even if the knee joint is a hinge joint (Fig. 8-46), medial and lateral rotations minutely occur together with the hip joint rotation (Fig. 8-45).

< Foot >



In the foot, many bones and synovial joints relieve the impact.



The bones of foot configurate the longitudinal and transverse arches of the foot.



The longitudinal and transverse arches remind us of the Roman arches.



Muscles of the sole are organized in four layers. So as to memorize the muscles, a love affair is introduced. Three female matchmakers (2nd, 3rd, and 4th toes) encourage a good relationship between Ms. Mini (little toe) and Mr. Hall (great toe).

In the 1st round (layer), matchmakers bow (flexor digitorum brevis); shy Ms. Mini also bows (flexor digitorum brevis) (It is not drawn in the comic strip because the flexor digitorum brevis to the little toe occasionally does not exist like the extensor digitorum brevis to the little toe does not exist (Fig. 8-30).) but goes away (abductor digiti minimi) and Mr. Hall goes away (abductor hallucis) too.

In the 2nd round, the disappointed matchmakers and Ms. Mini frown like as if they are chewing worms (lumbrical muscles; Latin word “lumbricus” means worm.), whilst sitting on the rectangular table (quadratus plantae).

In the 3rd round, Ms. Mini bows (flexor digiti minimi brevis) and Mr. Hall bows (flexor hallucis brevis) too and comes closer (adductor hallucis) in a manly manner.

In the last 4th round, Ms. Mini and matchmakers constantly gather and dismiss (plantar and dorsal interossei) to prepare for a wedding.

Two extrinsic muscles (flexor digitorum longus, flexor hallucis longus) not mentioned in the comic strip pass in the 2nd and 3rd layers, respectively (Figs. 8-37,40,41).


Fig. 8-39. First layer of sole.


Fig. 8-40. Second layer of sole.


The flexor digitorum brevis (1st layer) and longus (2nd layer) are homologous with the flexor digitorum superficialis and profundus of the upper limb (Fig. 2-38). The flexor digitorum brevis splits and ends at the middle phalanges, whereas the flexor digitorum longus passes and ends at the distal phalanges (Fig. 8-36). The pattern is same as the hand (Fig. 2-39).

In the hand, the lumbrical muscles start from the flexor digitorum profundus. Likewise, in the foot, the lumbrical muscles start from the flexor digitorum longus (2nd layer). The insertion of the lumbrical muscles (extensor expansion) and action are identical to those in the hand (Fig. 2-57).

The flexor digitorum longus is not only the origin of the lumbrical muscles, but also the insertion of the quadratus plantae. If there were no quadratus plantae, the flexor digitorum longus passing the flexor retinaculum which is shifted medially would move the toes to the medial side (Fig. 8-28). Therefore, the foot requires the quadratus plantae; but the hand does not need such a muscle, since the flexor retinaculum is not shifted to any particular side (Fig. 2-52).



There are four Quadratus brothers who live apart: Quadratus Lumborum in the posterior abdominal wall (Fig. 6-54), Quadratus Femoris in the gluteal region (Fig. 8-17), Quadratus Plantae in the sole (Fig. 8-40), and Pronator Quadratus in the forearm (Fig. 2-41).


Fig. 8-41. Third layer of sole.


The 3rd layer includes three intrinsic muscles to move the great and little toes and an extrinsic muscle, the flexor hallucis longus. The flexor hallucis longus has no attachment to the intrinsic muscles, unlike the flexor digitorum longus in the 2nd layer (Fig. 8-40). It is probably because Harry (flexor Hallucis longus) (Fig. 8-37) is too nervous to get in close contact with companions.

(The confused students do not have to read the next five paragraphs.)

Let us consider the 1st and 3rd layers’ muscles as being correspondent to thenar and hypothenar eminence muscles of the palm.

First, the abductor hallucis (1st layer) (Fig. 8-39) corresponds to the abductor pollicis brevis; the flexor hallucis brevis (3rd layer) to the flexor pollicis brevis; and the adductor hallucis (3rd layer) to the adductor pollicis, even if the adductor pollicis is not a thenar eminence muscle in fact (Fig. 2-54).

Second, the flexor hallucis brevis (3rd layer) arrives at the proximal phalanx like the flexor pollicis brevis (Fig. 2-54); the flexor hallucis longus (3rd layer) arrives at the distal phalanx just as the flexor pollicis longus (Fig. 2-40).

Third, the flexor digiti minimi brevis in the sole (3rd layer) and the flexor digiti minimi brevis in the palm are different muscles despite their same name (Fig. 2-55). Just as is in the hand, there is no flexor digiti minimi longus in the foot. Instead, its function is performed by the little toe parts of the flexor digitorum longus (Fig. 8-36) and flexor digitorum brevis (Fig. 8-39).

Lastly, the sole has all muscles equivalent to thenar and hypothenar eminence. The only exception is the opponens muscles because we do not need the opposition of great and little toes.



Fig. 8-42. Fourth layer of sole.


Abduction and adduction of the toes occur based on the 2nd metatarsal bone, which is determined by the routes of the plantar and dorsal interossei. As previously mentioned, inversion and eversion also occur depending on the 2nd metatarsal bone (Fig. 8-33).

In summary, the 2nd metatarsal bone in the center of the foot (Fig. 8-41) acts as the guideline for the motion of the toes and ankle. Comparatively, the 3rd metacarpal bone in the center of hand is the guideline for the motion of the fingers (Fig. 2-60) and wrist (Fig. 2-47).




There is another way to remember the four layers. Which is your favorite?

Fig. 8-43. Sole skin innervated by two nerves.


Internal to the flexor retinaculum, the tibial nerve (Fig. 8-37) divides into the medial and lateral plantar nerves. The sole skin is innervated by the two nerves, of which the border passes the 4th toe. It can be said that medial and lateral plantar nerves are homologous with the median and ulnar nerves, respectively (Fig. 2-61). The deep fibular nerve (Fig. 8-37), responsible for the skin of dorsum of foot, is homologous with the radial nerve (Fig. 2-61).

Just as the median and ulnar nerves innervate the palm muscles, the medial and lateral plantar nerves innervate the sole muscles.



The MEat LoAF mnemonics can also be used for the innervation of the medial plantar nerve. In other words, the muscles, innervated by the medial plantar nerve, correspond to the muscles, innervated by the median nerve (Fig. 2-52).

The 1st lumbrical muscle of the foot (Fig. 8-40) corresponds to the 1st and 2nd lumbrical muscles of the hand (Fig. 2-57) (Do not ask the authors why they differ.), the abductor hallucis (Fig. 8-39) to the abductor pollicis brevis (Fig. 2-54), the flexor hallucis brevis (Fig. 8-41) to the flexor pollicis brevis (Fig. 2-54), and the flexor digitorum brevis (Fig. 8-39) to the flexor digitorum superficialis (Fig. 2-38). The conspicuous difference is that the flexor digitorum brevis is an intrinsic muscle of the foot whereas the flexor digitorum superficialis is an extrinsic muscle of the hand.


Fig. 8-44. Arteries of foot.


The anterior tibial artery (Fig. 8-37) becomes the dorsal artery of foot (dorsalis pedis artery) once it passes the ankle joint. The dorsal artery of foot bifurcates into the 1st dorsal metatarsal artery and the deep plantar artery. The arcuate artery which is a branch of the dorsal artery of foot gives off the 2nd–4th dorsal metatarsal arteries.

Meanwhile, the posterior tibial artery (Fig. 8-37) divides into the medial and lateral plantar arteries just as the tibial nerve divides into the medial and lateral plantar nerves (Fig. 8-43).

The plantar arch is made of the deep plantar artery and lateral plantar artery to allow for anastomosis. The plantar arch giving rise to the plantar metatarsal arteries is equivalent to the deep palmar arch giving rise to the palmar metacarpal arteries (Fig. 2-63). On the other hand, the arcuate artery (branches: dorsal metatarsal arteries) is equivalent to the dorsal carpal arch (branches: dorsal metacarpal arteries) that is not illustrated in the hand chapter.

< Hip and knee joints >


The hip and knee joints where the body weight is loaded most heavily are vulnerable to diseases, so they are very important in orthopedics. However, after hurried dissection by students, only the following structures can be identified in the two joints.


Fig. 8-45. Hip joint.


In case of the hip joint, the acetabular labrum and the ligament of head of femur are worth discovering. The acetabular labrum makes a shallow bone structure (acetabulum of hip bone) deep to stabilize the ball and socket joint. Similarly in the shoulder joint, the glenoid labrum deepens the glenoid cavity of scapula (Fig. 2-25).

In the hip joint, the articular surfaces are the lunate surface (a part of acetabulum) and the head of femur.



Keep an eye on the epicondyles in the humerus (Fig. 2-33) and femur as well as on the condyles in the femur and tibia (Fig. 8-46).



In the knee joint, two articular menisci imperfectly divide the articular cavity (Fig. 2-59) unlike the articular disc (Fig. 4-17).



The meniscus of the knee joint (Fig. 8-46) as well as the lunate surface of the hip joint resembles a crescent moon.


Fig. 8-46. Knee joint.


The lateral meniscus is apart from the fibular collateral ligament which approaches the head of fibula. However, the medial meniscus is attached to the tibial collateral ligament. When the tibial collateral ligament is strained past the normal range, the medial meniscus can be torn.



A doubtful hypothesis is introduced. If ellipsoid and round structures coexist, the ellipsoid one is attached to the more meaningful structure. The medial meniscus to the tibial collateral ligament (Fig. 8-46), the oval window to the stapes (Fig. 4-51), the utricle to the three semicircular ducts (Fig. 4-56), and the foramen ovale to the motor nerve of V3 (Fig. 4-21).



The anterior and posterior cruciate ligaments are named according to their attachment to the tibia (Fig. 8-46).



The posterior movement (retraction and flexion) of tibia is limited by the posterior cruciate ligament. Reversely, the anterior movement (protraction and hyperextension) of the tibia is restricted by the anterior cruciate ligament.



Bird and animal with four legs walk on their tiptoes. Their knee joints are commonly hidden close to the trunk.

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