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1.3.21 Skin of the hand, fingernails

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(2.59)

Last of all, we’ll take a look at the skin of the hand, and at the fingernails. On the back of the hand the skin is thin, and freely movable. This underlying layer of loose areolar tissue enables the skin to move. When the wrist and the MP joints are extended, the skin is loose and redundant. When they’re flexed, it becomes tight.

By contrast, the skin on the front of the hand is quite thick, and much less movable. It’s fixed to the underlying palmar aponeurosis by many strands of tough fibrous tissue. The creases on the palmar skin are lines along which the skin is thinner. The creases act as joints in the skin when the MP joints flex.

It’s easy to see where the MP joints are when we look at the back of the hand. But because of the way the skin slopes forward in between the bases of the fingers, the position of the MP joints can be a surprise, when we’re looking from the front of the hand. The MP joints aren’t here, they’re right back here, in line with the distal palmar skin crease.

So fully half the length of the proximal phalanx of each finger lies beneath the skin of the palm. On the fingers, as in the hand, the skin is thin and extensible on the back, thick and deeply creased on the front. Let’s take a close look at the specialized skin of the fingertip.

The skin of the fingertip contains huge numbers of sensory nerve endings. The pulp of the fingertip is composed of fat, interlaced with many fibrous strands which anchor the skin to the distal phalanx.

The fingernail is a hard plate of keratin that’s produced by the specialized epithelial cells which lie beneath its base, ...

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(2.59)

Last of all, we’ll take a look at the skin of the hand, and at the fingernails. On the back of the hand the skin is thin, and freely movable. This underlying layer of loose areolar tissue enables the skin to move. When the wrist and the MP joints are extended, the skin is loose and redundant. When they’re flexed, it becomes tight.

By contrast, the skin on the front of the hand is quite thick, and much less movable. It’s fixed to the underlying palmar aponeurosis by many strands of tough fibrous tissue. The creases on the palmar skin are lines along which the skin is thinner. The creases act as joints in the skin when the MP joints flex.

It’s easy to see where the MP joints are when we look at the back of the hand. But because of the way the skin slopes forward in between the bases of the fingers, the position of the MP joints can be a surprise, when we’re looking from the front of the hand. The MP joints aren’t here, they’re right back here, in line with the distal palmar skin crease.

So fully half the length of the proximal phalanx of each finger lies beneath the skin of the palm. On the fingers, as in the hand, the skin is thin and extensible on the back, thick and deeply creased on the front. Let’s take a close look at the specialized skin of the fingertip.

The skin of the fingertip contains huge numbers of sensory nerve endings. The pulp of the fingertip is composed of fat, interlaced with many fibrous strands which anchor the skin to the distal phalanx.

The fingernail is a hard plate of keratin that’s produced by the specialized epithelial cells which lie beneath its base, here. A fold of skin overlaps the edge of the nail, and adheres to it closely. We’ll remove the skin on one side, to see the full extent of the nail, here’s its edge; and we’ll take away one half of the nail, to see the underlying nailbed, or nail matrix.

Finally we’ll remove part of the nailbed, here’s the cut edge of the nailbed. It’s closely adherent to the underlying distal phalanx. The actual nail forming tissue is just here. It’s the nail forming tissue that produces this pale area, the lunula, that's visible at the base of many peoples’ nails.

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