The hand is the portion of the arm or anterior limb of a human or other primate, where the appendage terminates. This part of the limb is especially used in grasping and holding. Each hand is a mirror image of the other.

What constitutes a Hand?

Although many mammals and other animals have grasping appendages similar in form to a hand, these are scientifically not considered to be so, and have other varying names, including paws. Using the term hand is merely a scientific usage of anthropomorphization, to distinguish the terminations of the front paws from the hind ones. The only true hands appear in the mammalian order of primates. Hands must also feature opposable thumbs, as described later in the text.

Human anatomy of the hand

The human hand consists of a broad palm (metacarpus) with five digits, attached to the forearm by a joint called the wrist (carpus).

Digits

The Five Fingers

Five fingers on the hand are located at the outermost edge of the palm. These four digits can be folded over the palm, this allows for the holding of objects, and furthermore the grasping of small objects. Each finger, starting with the one closest to the thumb, has a colloquial name to distinguish it from the others:

Thumb
Index finger, pointer finger, or forefinger
Middle finger
Ring finger
Little finger or 'pinky'

The thumb (connected to the trapezium) is located on one of the sides, parallel to the arm. The thumb can be easily rotated 90º, on a perpendicular level compared to the palm, unlike the fingers which can only be rotated approximately 45º. A reliable way of identifying true hands is from the presence of opposable thumbs. Opposable thumbs are identified by the ability to be brought opposite to the fingers.

Bones

The human hand has at least 27 bones: the carpus or wrist account for 8; the metacarpus or palm contains 5; the remaining 14 are digital bones.

Bones of the wrist

The wrist has eight bones, arranged in two rows of four. These bones fit into a shallow socket formed by the bones of the forearm.

Bones of the palm

The palm has 5 bones, one to each of the 5 digits.

Digital bones

Also called phalanx bones. Human hands contain 14 of them; 2 in the thumb, and 3 in each of the four fingers, called;

Distal phalanx, carrying the nail,

Middle phalanx and

Proximal phalanx.

(The thumb has no middle phalanx).

Sesamoid bones

Sesamoid bones are small ossified nodes embedded in the tendons to provide extra leverage and reduce pressure on the underlying tissue. Many exist around the palm at the bases of the digits, but the exact number varies between different people. The patella is the largest example of a sesamoid bone in the human body.

Muscles and tendons

The movements of the human hand are accomplished by two sets of each of these tissues. They can be subdivided into two groups: the extrinsic and intrinsic muscle groups. The extrinsic muscle groups are the long flexors and extensors. They are called extrinsic because the muscle belly is located on the forearm.

Intrinsic hand muscles

The Intrinsic muscle groups are the thenar and hypothenar muscles (thenar referring to the thumb, hypothenar to the small finger), the interosseus muscles (between the metacarpal bones, four dorsally and three volarly) and the lumbrical muscles. These muscles arise from the deep flexor (and are special because they have no bony origin) and insert on the dorsal extensor hood mechanism.

The extrinsic muscles of the hand

The flexors: The fingers have two long flexors, located on the underside of the forearm. They insert by tendons to the phalanges of the fingers. The deep flexor attaches to the distal phalanx, and the superficial flexor attaches to the middle phalanx. The flexors allow for the actual bending of the fingers. The thumb has one long flexor and a short flexor in the thenar muscle group. The human thumb also has other muscles in the thenar group (opponens- and abductor muscle), moving the thumb in opposition, making grasping possible.

The extensors: Located on the back of the forearm and a connected in a more complex way then the flexors to the dorsum of the fingers. The tendons unite with the interosseous and lumbrical muscles to form the extensor-hood mechanism. The primary function of the extensors is to straighten out the digits. The thumb has two extensors in the forearm; the tendons of these form the anatomical snuffbox. Also, the index finger and the little finger have an extra extensor, used for instance for pointing.

Variation

Some people have more than the usual number of fingers or toes, this is normally caused by a genetic condition called Polydactyly.

The name Phalanges is commonly given to the bones that form fingers and toes. In primates such as humans and monkeys, the thumb and big toe have two phalanges, while the other fingers and toes consist of three.

The phalanges do not really have individual names but are named after the digit, and their distance from the body. Distal phalanges are at the tips of the fingers and toes, the proximal phalanges are closest to the hand (or foot) and articulate with the metacarpals or metatarsals. Middle phalanges are between the distal and proximal. The thumb and big toe do not have middle phalanges.

The phalanges of the foot correspond with those of the hand. They differ from them in their size (the bodies being much reduced in length) and being laterally compressed.

First Row: The body of each is compressed from side to side, convex above, concave below. The base is concave; and the head presents a trochlear surface for articulation with the second phalanx.

Second Row: The phalanges of the second row are remarkably small and short, but rather broader than those of the first row.

The ungual phalanges, in form, resemble those of the fingers; but they are smaller and are flattened from above downward; each presents a broad base for articulation with the corresponding bone of the second row, and an expanded distal extremity for the support of the nail and end of the toe.

The phalanges are each ossified from two centers: one for the body, and one for the base. The center for the body appears about the tenth week, that for the base between the fourth and tenth years; it joins the body about the eighteenth year.

Pelvis

The pelvis is the bony structure located at the base of the spine (properly known as the caudal end). The pelvis incorporates the socket portion of the hip joint for each leg (in bipeds) or hind leg (in quadrupeds). It forms the lower limb (or hind-limb) girdle of the skeleton.

Human female pelvis, viewed from front

The pelvis is symmetrical and each side is actually made up of three separate bones - the upper half (the broad "wings") is the ilium; the middle (the top half of the lower "loops") is the pubis, and the bottom (the lower half of the "loops") is the ischium. These three bones fuse together with age and are collectively known as the hip bone, ossa coxae or the innominate bone. The pelvis is joined to the sacrum bone by ligaments (the sacroiliac joint), and the hip bones nest in specially shaped sockets (the acetabulum) on each side. The upper edge of the ilium is known as the iliac crest. The place at the front of the pelvis where the two sides join together is called the symphysis pubis. This is normally a very inflexible joint, but it softens and becomes more flexible during late pregnancy, allowing it to expand during labour for the baby's head to pass through. A female pelvis is also wider and shallower than a male pelvis.

A well-known way of determining the sex of a pelvis is to compare the angle of the width of the frontal opening to one's hand. If the angle is about the same as between the outstretched thumb and index finger, it is a female pelvis (arcus pubis). If it is closer to the angle between the spread index and middle fingers, it is a male pelvis (arcus subpubis).

The pelvis protects the digestive and reproductive organs in the lower part of the body, and many large nerves and blood vessels pass through it to supply the legs. It is also an important load-bearing part of the skeletal system.

Human leg

In common language a leg is the entire lower limb, including (at least) the thigh, the knee, and the calf. In the strict sense of human anatomy, the leg is the part of the lower limb that lies between the knee and the foot. This article follows the popular usage that includes the lower limb from hip to ankle, including the buttock and excluding the foot.

Long bones of the lower limb

Femur (thigh bone)
Patella (kneecap)
Tibia (shin bone)
Fibula (calf bone)

Muscles of the human lower limb

Muscles of the thigh

Anterior compartment of the thigh

Quadriceps femoris, which is composed of:

Vastus lateralis
Vastus medialis
Vastus intermedius
Rectus femoris
Sartorius
Adductor longus
Adductor brevis
Adductor magnus
Gracilis
Pectineus
Gluteus maximus
Tensor fascia lata

Posterior compartment of the thigh

Biceps femoris
Semimembranosus
Semitendinosus

Muscles of the calf

Popliteus
The anterior compartment
Tibialis anterior
Extensor digitorum longus
Extensor hallucis longus
Peroneus tertius
The posterior compartment
Gastrocnemius (attached to the calcaneus by Achilles' tendon)
Plantaris
Soleus
The lateral compartment
Peroneus longus
Peroneus brevis
The deep posterior compartment
Tibialis posterior
Flexor digitorum longus
Flexor hallucis longus

Vasculature of the leg

The arteries

Common femoral artery
Deep femoral artery
Superficial femoral artery
Popliteal artery
Anterior tibial artery
Posterior tibial artery
Peroneal artery
Arcuate artery

The veins

Greater saphenous vein
Lesser saphenous vein
Femoral vein
Popliteal vein
Anterior tibial vein
Posterior tibial vein
Peroneal vein

Foot

The foot is a biological structure found in many animals that is used for locomotion. The plural of foot is feet, and this pair is one of seven mutated English plurals.

Structure

The structural quality of a foot varies from animal to animal. Many vertebrates that have legs also have a foot located at the end of each leg. For these animals, the foot is a complex structure of bone, muscle, and other connective tissue. Among animals that have soft or padded feet, the foot is commonly called a paw. In mollusks, on the other hand, the foot is a purely muscular structure.

Parts of the foot

Ankle

Heel

Instep

Sole

Ball

Five toes

Common disorders of the feet

Athlete's foot

Bunion

Callus

Plantar wart

Ankle

In anatomy, the ankle is the part of the lower limb that is located between the foot and the leg, and is actually comprised of two separate joints: the talocrural joint (or "true" ankle joint) and the subtalar joint.

The talocrural joint, is a synovial joint that connects the distal ends of the tibia and fibula with the proximal end of the talus and is responsible for dorsiflexion and plantar flexion.

The subtalar joint connects the talus with the calcaneus and helps with inversion and eversion of the foot.

The ankle does not allow rotation.

Heel

The heel is the prominence at the posterior end of the foot. It is based on the projection of one bone, the calcaneus, behind the articulation of the bones of the lower leg. In the long-footed mammals, both the hoofed species (unguligrade) and the clawed forms which walk on the toes (digitigrade), the heel is well above the ground at the apex of the angular joint known as the hock. In plantigrade species it rests on the ground.

Sole

The Sole is the bottom of the foot. Much like the palm of the hand, it has thicker skin than most other parts of the body, and is relatively less pigmented. A set of creases formed in the womb criss-cross the sole. In anatomy, the sole of the foot is referred to as the plantar aspect.

Toes

Toes are the digits of the foot of a human or animal.

In humans, the toe includes the phalanges of the foot's skeleton; the bones of each toe continue all the way to the heel, although in from the base of the toes they are united in the body of the foot. The innermost toe (the leftmost one on the right foot, see picture) is by far the thickest (big toe, great toe, or hallux); the one on the other end is short and thin.

The toes, especially the big toe, play an essential role in walking, although a loss of the smallest toe will not affect gait.