Human Anatomy - Kotsan I. Y. 2009

Skeleton of the upper limb
Bones of the fingers

The hand comprises the thumb (pollex, digitus primus), index finger (index, digitus secundus), middle finger (digitus medius, tertius), ring finger (digitus annularis, quartus), and little finger (digitus minimus, quintus).

The BONES OF THE fingers, or Phalanges (phalanges digitorum), are short tubular bones. Each digit consists of three phalanges: the proximal (phalanx proximalis), middle (phalanx media), and distal (phalanx distalis) phalanx. An exception is the first digit (thumb), which has only two phalanges—proximal and distal. The proximal phalanges are the longest, while the distal ones are the shortest.

Each phalanx is divided into a base (basis phalangis), a shaft (corpus phalangis), and a HEAD (caput phalangis).

The Base of the proximal phalanges features a smooth, concave articular surface that articulates with the head of the corresponding metacarpal bone, whereas the bases of the middle and distal phalanges possess articular surfaces divided into two parts by a small elevation, connecting the phalanges to one another.

The shafts of the proximal and middle phalanges are convex on the dorsal side and slightly concave on the palmar side.

The heads of the proximal and middle phalanges bear pulley-like (trochlear) articular surfaces for interphalangeal articulation. The heads of the distal phalanges lack articular surfaces. The extremity of each distal phalanx is flattened, forming the tuberosity of the distal phalanx (tuberositas phalangis distalis).

In addition to the aforementioned bones, the hand also contains sesamoid bones. These are embedded within Muscle tendons and increase the moment arm of the Muscles Attached to them (most frequently found in the tendons supplying the thumb and index finger on the PALMAR ASPECT OF the hand).

The bones of the distal carpal row (trapezium, trapezoid, capitate, hamate) and the four Metacarpal bones (II–V) exhibit limited mobility relative to one another and are reinforced by a very strong ligamentous apparatus. Consequently, they function as a single structural unit—the rigid base of the hand, which is characterized by exceptional strength.

Inherited by early hominids from animal ancestors, the Skeletal Structure of the hand underwent transformation throughout Human Evolution under METABOLISM/18.html">The Influence of labor, resulting in several distinctive features characteristic of the modern human hand:

1. An increase in the absolute and relative dimensions (compared to the other fingers) of the bones of the first digit.

2. The saddle-shaped configuration of the first carpometacarpal joint.

3. The repositioning of the first digit from the plane of the other fingers in a palmar direction, thereby enhancing its capacity for opposition to the other digits via the saddle joint.

4. The Displacement of the Carpal Bones associated with the first digit (the trapezium and scaphoid) in the same palmar direction, resulting in a deepening of the carpal sulcus.

5. The shortening and straightening of the phalanges of digits II–V, which facilitates A wide variety of Movements of the hand and its individual parts.

Alongside this remodeling of Bones and joints, the neuromuscular apparatus of the hand also evolved. The overall Development of the Central Nervous system, driven by labor and articulate speech, transformed the upper limb—particularly its primary effector, the hand—into an organ of labor, an Organ of Touch, and, to some extent, a tool for communication (gesticulation).