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A primer on anatomy - Part 2

Each shoulder articulates with the proximal end of the humerus.

The distal end of the humerus articulates, via the elbow, with the proximal ends of the ulna and radius. The distal end of the radius articulates with the wrist.

The hand, or manus, is composed of the wrist, or carpus (eight small, oval-like bones called the carpals), the metacarpus (five metacarpals), and the phalanges (or fingers, comprised of 14 bones in each hand).

The main musculature

There are more than 600 muscles that move the skeleton and some soft tissues, such as the lips and eyelids. Movement is produced by contraction and relaxation of opposing muscle groups, at joints.

Calf muscles

Group of seven posterior muscles below the knee, divided into superficial and deep groups, whose functions include extending the ankle (pointing the toes). The two main muscles are the meaty two-headed gastrocnemius and, beneath it, the soleus. The gastrocnemius connects the heel to the femur, and the soleus connects the heel to the tibia and fibula — the gastrocnemius crosses the ankle and knee joints, while the soleus crosses the ankle joint only. The tendons of these two muscles, together with the plantaris, fuse to form the Achilles tendon.

Exercises that train the calves are calf raises.

Other muscles below the knee

There are four anterior muscles, which move the toes and foot — the largest is the tibialis anterior, which runs alongside the tibia. And two muscles extend along the lateral surface of the fibula — peroneus longus, and peroneus brevis, which lower and evert the foot.

Hamstrings

The three muscles of the rear thigh: biceps femoris (two-headed muscle), semitendinosus, and semimembranosus. They flex the knees, and contribute to hip extension (rearward movement of the femur). The hamstrings are abbreviated to hams.

The primary exercise that trains the hamstrings is the leg curl. Deadlifts, squats, leg press, and back extensions also work the hamstrings.

Quadriceps femoris

Group of four muscles of the frontal thigh: rectus femoris, vastus lateralis, vastus medialis, and vastus intermedius. The tendons of insertion of the four quadriceps muscles form the patella tendon.

The rectus femoris connects the tibia (through the patella) to the pelvis, whereas the other three connect the tibia (through the patella) to the femur. The rectus femoris flexes the femur (raises it) at the hip joint and extends the leg at the knee joint; the other three quadriceps muscles extend the leg only.

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