The Visible Human: Transverse Section Through the Thigh

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Introduction: This transverse section illustrates the muscle of the upper thigh. Different groups of muscles carry out opposing actions with regards to moving the hip and knee joints. Some muscles flex the hip (bringing the legs into the chest), extend the hip (kicking the leg behind the body), flex the knee (bending the knee) , extend the knee (straightening the knee), and adduct the hip (pressing the inside of the legs together). Abduction of the hip (kicking the leg out to the side) is carried out by the gluteal muscles which do not appear in this section.

Annotations

adductor_longus: The adductor longus is a muscle of the inner thigh. It adducts the hip, and action which brings the knees together, towards the midline of the body. This muscle receives heavy usage when riding a horse.

adductor_magnus: As its name suggests, the adductor magnus (magnus=large) is the largest adductor muscle of the thigh. It helps press the knees together, an action that aDducts the hip joint.

fashia: Note the fatty tissue surrounding the leg. This layer of fat helps insulate the body. It can also be metabolized during period of starvation to provide the body with a source of energy.

femur: The femur is the 'long bone' of the thigh. Many muscles attach near the end of that inserts into the hip socket (greater trochanter). The head of the femur is covered with smooth cartilage to allow for frictionless movement within the joint. The distal end of the femur forms the medial and lateral condyles that associate with the kneecap, or patella. The condyles can be felt by bending the knee and pressing a little above your knee on either side. The 'lumps' are the condyles.

The femur has a hollow interior. This region contains fat and bone marrow. Blood cells including erythrocytes (red blood cells) and white blood cells develop in the marrow. Once developed they enter the blood to carry oxygen or help protect the body against infection.

gracilis: The gracilis is one of the adductors of the hip - muscles that draw the knees together, often used to stay on horses. It runs from the lower edge of the hip to just below the knee.

great_saphenous_vein: The great saphenous vein is one of the larger superficial veins of the leg. Pieces of this vein are commonly used as grafts for heart bypass operations.

hamstring: The semimembranous, semitendinous and biceps femoris muscles form the hamstring. This muscle runs along the back of the leg, from behind the knee to below the buttocks. These three muscle both flex the knee (bend it), and extend the hip (kick the leg behind the body). These muscles contract very strongly when bending forward to keep you from falling forward. You can feel the tendon of the semimembranous muscle by placing a hand over the inside of the leg, just above and behind the knee, while bending the knee. The tendon for the biceps femoris muscle may be felt in the same region on the outside of the leg.

marrow: The whitish area in the middle of the femur contains the bone marrow (a favorite in French soups!). Blood cells develop in this area. These cells include erythrocytes - red blood cells, immune cells such as macrophages, and lymphocytes, and platelets. Platelets are small pieces of larger cells called megakaryocytes (mega=big; karyon=nucleus; cyte=cell). As their name implies, these cells are very large and have a big nucleus. As the cells develop they shed pieces of membrane that enter the circulation as platelets. The platelets help seal broken blood vessels, forming clots when you get a cut.

rectus_femoris: Running a finger from just above the knee to just below the hip approximately traces the location of the rectus femoris muscle. This muscle both extends the knee (straightens it out), and flexes the hip joint (bringing the knees into the chest). When your knee 'jumps' at the doctor's office, the reflex tested causes the rectus femoris to contract suddenly, thus causing the knee jerk.

sartorius: Trace a path from the outside of the hip to a spot just below the inside of your knee. This path outlines the general location of the sartorius muscle. This muscle is a weak flexor of the hip. We tend to use it more when sitting Indian style, or in the 'Lotus position.'

vastus_intermedius :

vastus_lateralis :

vastus_medialis :

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