The hand skeleton is made of 27 bones divided into three groups.

1. The CARPUS corresponds to the wrist.
2. The METACARPUS corresponds to the hand.
3. The PHALANGES correspond to the fingers.

The carpus

The carpus consists of eight bones, arranged in two rows, four bones in each row. Enumerated from the radial to the ulnar side, the bones of the proximal row are named navicular (scaphoid), lunate (semilunar), triquetral (cuneiform), and pisiform; those of the distal row, greater multangular (trapezium), lesser multangular (trapezoid), capitate (os magnum), and hamate (unciform).

When the bones of the carpus are articulated, they form a mass somewhat quadrangular in outline, wider below than above, and with the long diameter transverse. The dorsal surface is convex and the volar surface concave from side to side. The concavity is increased by four prominences, which project forward, one

 

Bones of the Left Hand. (Dorsal surface.)

 from each extremity of each row. On the radial side are the tuberosity of the navicular and the ridge of the greater multangular; on the ulnar side, the pisiform and the hook of the hamate. Stretched transversely between these prominences, in the recent state, is the transverse carpal ligament forming a canal for the passage of the flexor tendons and the median nerve into the palm of the hand. The proximal border of the carpus is convex and articulates with the distal end of the radius and the articular disc. The pisiform, however, takes no share in this articulation, being attached to the volar surface of the triquetral. The distal border forms an undulating articular surface for the bases of the metacarpal bones. The line of articulation between the two rows of the carpus is concavo-convex from side to side, the lateral part of the navicular being received into the concavity formed by the greater multangular, lesser multangular, and capitate, and the capitate and hamate into that formed by the navicular, lunate, and triquetral bones.

Bones of the Left Hand. (Volar surface.)

The individual carpal bones have several points of resemblance. Each bone (excepting the pisiform) has six surfaces, of which the anterior or volar and posterior or dorsal are rough for the attachment of ligaments, the volar surface being the broader in the proximal row, the dorsal surface in the distal row. The superior and inferior surfaces are articular, the former being generally convex and the latter concave. The lateral surfaces, when in contact with adjacent bones, are also articular, but otherwise rough for the attachment of ligaments. Further, the whole of the carpus is cartilaginous at birth and each bone is ossified from a single center.

The Navicular

The navicular [os naviculare] or scaphoid is the largest bone of the proximal row, and so disposed that its long axis runs obliquely downward and lateralward.

The superior surface is convex and somewhat triangular in shape for articulation with the lateral facet on the distal end of the radius. The inferior surface, smooth and convex, is divided into two parts by a ridge running from before backward. The lateral part articulates with the greater multangular, the medial with the lesser multangular. The volar surface, rough and concave above, is elevated below into a prominent tubercle for the attachment of the transverse carpal ligament and the abductor pollicis brevis. The dorsal surface is narrow, being reduced

 

The Left Navicular

to a groove running the whole length of the bone; it is rough and serves for the attachment of the dorsal radio-carpal ligament. The medial surface is occupied by two articular facets, of which the upper is crescentio in shape for the lunate bone, whilst the lower is deeply concave for the reception of the head of the capitate. The lateral surface is narrow and rough for the attachment of the radial collateral ligament of the wTist-joint.

Articulations

With the radius above, greater and lesser multangular below, lunate and capitate medially.

The Lunate

The lunate [os luuatum] or semilunar, placed in the middle of the proximal row of the carpus, is markedly crescentic in outline.

The superior surface is smooth and oonve.x and articulates with the medial of the two facets on the distal end of the radius. The inferior surface presents a deep concavity divided into two parts by a line running from before backward. Of these, the lateral and larger articulates with the capitate; the medial and smaller with the hamate. The volar surface is large and convex,

The Left Lunate.

the dorsal surface narrow and flat, and both are rough for the attachment of ligaments. The medial surface is marked by a smooth quadrilateral facet for the base of the triquetral. The lateral surface forms a narrow crescentic articular surface for the lunate.

Articulations

With the radius above, capitate and hamate below, navicular laterally and triquetral medially.

The Triquetral

The triquetral [os triquetrum] or cuneiform is pyramidal in shape and placed obliquely, so that its base looks upward and laterallj^ and the apex downward and medially.

The Left Triquetral.

The superior surface presents laterally near the base a small, convex articular facet which plays upon the articular disc interposed between it and the distal end of the ulna, and medially a rough non-articular portion for ligaments. The inferior surface forms a large, triangular undulating facet for articulation with the hamate. The volar surface can be readily recognised by the conspicuous oval facet near the apex for the pisiform bone. The dorsal surface is rough for the attachment of ligaments. The medial and lateral surfaces are represented by the base and the apex of the pyramid. The base is marked by a flat quadrilateral facet for the lunate. The apex forms the lowest part of the bone and is roughened for the attachment of the ulnar collateral ligament of the WTist.

Articulations

With the pisiform in front, lunate laterally, hamate below, articular disc above.

The Pisiform

The pisiform [os pisiforme], the smallest of the carpal bones, is in many of its characters a complete contrast to the rest of the series. It deviates from the general type in its shape, size, position, use, and development. Forming a rounded bony nodule with the long axis directed vertically, it is situated on a plane in front of the oth^r bones of the carpus.

The Left Pisiform.

On the dorsal surface is a single articular facet for the triquetral which reaches to the upper end of the bone, but leaves a free non-articular portion below. The volar surface, rough and rounded, gives attachment to the transverse carpal ligament, the flexor carpi ulnaris, the abductor quinti digiti, the piso-metacarpal and the piso-hamate ligaments. The median and lateral surfaces are also rough and the lateral presents a shallow groove for the ulnar artery. It is usually considered that the pisiform is a sesamoid bone developed in the tendon of the ^ea;or carpi ulnaris, though by some writers it is regarded as part of a rudimentary digit.

The Greater Multangular

The greater multangular [os multangulum majus] or trapezium, situated between the navicular and first metacarpal, is oblong in form with the lower angle prolonged downward and medially.

The Left Greater Multangular.

 The superior surface is concave and directed upward and medially for articulation with the lateral of the two facets on the distal surface of the navicular, and on the inferior surface is a saddle-shaped facet for the base of the first metacarpal. The volar surface presents a prominent ridge with a deep groove on its medial side which transmits the tendon of the^exor carpi radialis. The ridge gives attachment to the transverse carpal ligament, the abductor pollicis brevis, the opponens pollicis, and occasionally a tendinous slip of insertion of the abductor pollicis longus. The dorsal and lateral surfaces are rough for ligaments. The medial surface is divided into two parts by a horizontal ridge. The upper and larger portion is concave and articulates with the lesser multangular; the lower - a small flat facet on the projecting lower angle - articulates with the base of the second metarcarpal.

Articulations

With the navicular above, first metacarpal below, the lesser multangular and second metacarpal on the medial side.

The Lesser Multangular

The lesser multangular [os multangulum minus] or trapezoid, the smallest of the bones in the distal row, is somewhat wedge-shaped, with the broader end dorsally and the narrow end ventrally.

The Left Lesser Multangular.

The superior surface is marked by a small, quadrilateral, concave facet, for the media of the two facets on the lower surface of the navicular. The inferior surface is convex from side to side and concave from before backward, forming a saddle-shaped articular surface for the base of the second metacarpal. Of the volar and dorsal surfaces, the former is narrow and rough. the latter broad and rounded, constituting the widest sui-face of the bone, and both are rough for the attachment of ligaments. The lateral surface slopes downward and medially and is convex for articulation with the corresponding surface of the greater multangular. On the medial surface in front is a smooth flat facet for the capitate; elsewhere it is rough for ligaments.

Articulations

With the navicular above, second metacarpal below, greater multangular laterally, and the capitate medially.

The Capitate

The capitate [os capitatum] or os magnum is the largest bone of the carpus. Situated in the center of the wrist, the upper expanded portion, globular in shape and known as the head, is received into the concavity formed above by the navicular and lunate. The cubical portion below forms the body, whilst the intermediate constricted part is distinguished as the neck.

The Left Capitate.

Of the six surfaces, the superior is smooth and convex, elongated from before backward for articulation with the concavity of the lunate bone. The inferior surface is divided into three unequal parts by two ridges. The middle portion, much the larger, articulates with the base of the third metacarpal; the lateral, narrow and concave, looks lateral as well as downward to articulate with the second metacarpal, whilst the medial portion is a small facet, placed on the projecting angle of the bone dorsally, for the fom'th metacarpal bone. The volar surface is convex and rough, giving origin to fibers of the oblique adductor pollicis; the dorsal surface is broad and deeply concave. Thelateral surface presents, from above downward:

1. a smooth convex surface, forming the outer aspect of the head, with the superior surface of which it is continuous, for articulation with the navicular;
2. a groove representing the neck, indented for ligaments;
3. a small facet, flat and smooth, for articulation with the lesser multangular. Behind this facet is a rough area for attachment of an interosseous ligament. The medial surface has extending along its whole hinder margin an oblong articular surface for the hamate; the lower part of this smooth area sometimes forms a detached facet. The volar part of the surface is rough for an interosseous ligament.

Articulations

With the lunate and navicular above, second, third, and fourth metacarpals below, lesser multangular laterally, and hamate medially.

The Hamate

The hamate [os hamatum] or unciform is a large wedge-shaped bone, bearing a hook-like process, situated between the capitate and triquetral, with the base directed downward and resting on the two medial metacarpals.

The Left Hamate.

The apex of the wedge forms the narrow superior surface, directed upward and laterally for articulation with the lunate. The inferior surface or base is divided bj' a ridge into two (juadrilateral facets for the fourth and fifth metacarpal bones. The volar svu-face is triangular in outline and presents at its lower part a prominent hamulus (unciform process), a hook-like eminence, projecting forward and curved toward the carpal canal. It is flattened from side to side so as to present two surfaces, two borders, and a free extremity. To the latter the transverse carpal ligament and the flexor carpi ulnaris (by means of the piso-hamate ligament) are attached, whilst the medial surface affords origin to the flexor brcvis and the opponens digili quinli. The lateral surface is concave and in relation to the flexor tendons. The dorsal surface is triangular and rough for ligaments. The lateral surface has extending along its upper and hinder edges a long flat surface, wider above than below, for articulation with the capitate. In front of this articular facet the surface is rough for the attachment of an interosseous ligament. The medial surface is oblong and undulating, i. e., concavo-conve.x from base to apex, for articulation with the triquetral.

Articulations

With the triquetral, lunate, capitate, and the fourth and fifth metacarpal bones.

Ossification of the Carpal Bones

Capitate	first year	Greater multangular	fifth year
Hamate	second year	Navicular	sixth year
Triquetral	third year	Lesser multangular	eighth year
Lunate	fourth year	Pisiform	twelfth year

  

Additional carpal elements are occasionally met with. The os centrale occurs normally in the carpus of many mammals, and in the human fcetus of two months it is present as a small cartilaginous nodule which soon becomes fused with the cartilage of the navicular. Failure of fusion, with subsequent ossification of the nodule, leads to the formation of an os centrale in the human carpus which is then found on the dorsal aspect, between the navicular, capitate, and lesser multangular. In most individuals, however, it coalesces with the navicular or under-goes suppression.

An additional center of ossification, leading to the formation of an accessory carpal element, occasionally appears in connection with the greater multangular and the hamate. An accessory element {os Vesalianum) also occurs occasionally in the angle between the hamate and the fifth metacarpal, and others occur between the second and third metacarpals and the lesser multangular and capitate.

The metacarpals

The metacarpus consists of a series of five cylindrical bones [ossa metacarpalia], well described as 'long bones in miniature.' Articulated with the carpus above, they descend, slightly diverging from each other, to support the fingers, and are numbered from the lateral to the medial side. With the exception of the first, which in some respects resembles a phalanx, they conform to a general type.

A typical metacarpal bone presents for examination a shaft and two extremities. The body or shaft is prismatic and curved so as to be slightly convex toward the back of the hand. Of the three surfaces, two are lateral in position,

The First (Left) Metacarpal.

separated in the middle part of the shaft by a prominent palmar ridge, and concave for the attachment of interosseous muscles. The third or dorsal surface presents for examination a large, smooth, triangular area with the base below and apex above, covered in the recent state by the extensor tendons of the fingers, and two sloping areas, near the carpal extremity, also for interosseous muscles. The triangular area is bounded by two hnes, which commence below in two dorsal tubercles, and, passing upward, converge to form a median ridge situated between the sloping areas on either side. A little above or below the middle of the shaft, and near the volar border, is the medullary foramen, entering the bone obliquely upward. The base or carpal extremity, broader behind than in front, is quadrilateral, and both palmar and dorsal surfaces are rough tor ligaments; it articulates above with the carpus and on each side with the adjacent metacarpal bones. The head [capitulum] or digital extremity presents a large rounded articular surface, extending further on the palmar than on the dorsal aspect, for articulation with the base of the first phalanx. The volar surface is grooved for the flexor tendons and raised on each side into an articular eminence. On each side of the head is a prominent tubercle, and immediately in front of this a wellmarked fossa, to both of which the collateral ligament of the metacarpo-phalangeal joint is attached.

The Second (Left) Metacarpal.

 The second is the longest of all the metacarpal bones, and the third, fourth, and fifth successively decrease in length. The several metacarpals possess distinctive characters by which they are readily identified.

The first metacarpal is the shortest and widest of the series.

Diverging from the carpus more widely than any of the others the palmar surface is directed medially and marked

The Third (Left) Metacarpal.

a ridge placed nearer to the medial border. The lateral portion of the surface slopes gently to the lateral border and gives attachment to the opponens poUicis; the medial portion, the smaller of the two, slopes more abruptly to the medial border, is in relation to the deep head of the flexor pollicis brevis, and presents the nutrient foramen, directed downward toward the head of the bone and transmitting a branch of the arteria princeps poUicis. The dorsal surface, wide and flattened, is in relation to the tendons of the extensor poUicis longus and brevis.

The base presents a saddle-shaped articular surface for the greater multangular, prolonged in front into a thin process. There are no lateral facets, but laterally a small tubercle receives the insertion of the abductor pollicis longus. Medially is a rough area from which fibers of the inner head of the flexor pollicis brevis take origin. The margin of the articular surface gives attachment to the articular capsule of the carpo-metacarpal joint. The inferior extremity or head is rounded and articular, for the base of the first phalanx; the greatest diameter is from side to side and the surface is less convex than the corresponding surface of the other metacarpal bones. On the volar surface it presents two articular eminences corresponding to the two sesamoid bones of the thumb. Of the two margins, the medial gives origin to the lateral head of the first dorsal interosseous, the lateral receives fibers of insertion of the opponens pollicis.

The Fouhth (Left) Metacarpal.

The second metacarpal

The distinctive features of the four remaining metacarpals are almost exclusively confined to the carpal extremities. The second is easily recognised by its deeply cleft base. The terminal surface presents three articular facets, arranged as follows, from lateral to medial border:

1. a small oval facet for the greater multangular;
2. a hollow for the lesser multangular; and
3. an elongated ridge for the capitate.

The dorsal surface is rough for the insertions of the extensor carpi radialis longus and a part of the extensor carpi radialis brevis; the palmar surface receives the insertion of the flexor carpi radialis and gives origin to a few fibers of the oblique adductor pollicis. The lateral aspect of the extremity is rough and non-articular; the medial surface bears a bilobed facet for the third metacarpal.

The Fifth (Left) Metacarpal.

The shaft of the second metacarpal gives attachment to three interosseous muscles, and the nutrient foramen, directed upward on the ulnar side, transmits a branch of the second volar metacarpal artery.

The third metacarpal is distinguished by the prominent styloid process projecting upward from the lateral and posterior angle of the base. Immediately below it, on the dorsal surface, is a rough impression for the extensor carpi radialis brevis. The carpal surface is concave behind and convex in front, and articulates with the middle of the three facets on the inferior surface of the capitate. On the lateral side is a bilobed articular facet for the second metacarpal, and on the medial side two small oval facets for the fourth metacarpal. The volar a.spect of the base is rough and gives attachment to fibers of the oblique adductor pollicis and sometimes a slip of insertion of the flexor carpi radialis. The shaft of the third metacarpal serves for the origin of the transverse adductor pollicis and two interosseous muscles. The nutrient foramen is directed upward on the radial side and transmits a branch of the second volar metacarpal artery.

The fourth metacarpal has a small base. The carpal surface presents two facets: a medial, large and flat, for articulation with the hamate, and a small facet, at the lateral and posterior angle, for the capitate. On the lateral side are two small oval facets for the corresponding surfaces on the third metacarpal and a single concave facet on the medial side for the fifth metacarpal. The shaft of the fourth metacarpal gives attachment to three interosseous muscles, and the nutrient foramen, directed upward on the radial side, transmits a branch of the third volar metacarpal artery.

The fifth metacarpal is distinguished by a semilunar facet on the lateral side of the base for the fourth metacarpal, and a rounded tubercle on the medial side for the extensor carpi ulnaris, in place of the usual medial facet. The carpal surface is saddle-shaped for the hamate; the palmar surface is rough for ligaments including the piso-metacarpal prolongation from the flexor carpi ulnaris. The dorsal surface of the shaft presents an oblique line separating a lateral concave portion for the fourth dorsal interosseous muscle from a smooth medial portion covered by the extensor tendons of the little finger. The palmar surface gives attachment laterally to the third palmar interosseous muscle and medially to the opponens digili quinti. The nutrient foramen is directed upward on the radial side and transmits a branch of the fourth volar metacarpal artery.

The phalanges

The phalanges are the bones of the fingers, and number in all fourteen. Each finger consists of three phalanges distinguished as first or proximal, second

The Phalanges op the Third Digit op the Hand. (Dorsal view.) [The arrows indicate the direction of the nutrient canals.]

or middle, and third or distal. In the thumb, the second phalanx is wanting. Arranged in horizontal rows, the phalanges of each row resemble one another and differ from those of the other two rows. In all the phalanges the nutrient canal is directed downward, toward the distal extremity.

First phalanx

The shaft of a phalanx from the first row is flat on the palmar surface, smooth and rounded on the dorsal surface, i. e., semi-cyUndrical in shape. The borders of the palmar surface are rough for the attachment of the sheaths of the flexor tendons. The base or metacarpal extremity presents a single concave articular surface, oval in shape, for the convex head of the metacarpal bone. The distal extremity forms a pulley-like surface, grooved in the center and elevated at each side to form two miniature condyles, for articulation with the base of a second phalanx.

Second phalanx

The second phalanges are four in number and are shorter than those of the first row, which they closely resemble in form. They are distinguished, however, by the articular surface on the proximal extremity, which presents two shallow depressions, separated by a ridge and corresponding to the two condyles of the first phalanx. The distal end for the base of the third phalanx is trochlear or pulley-like, but smaller than that of the first phalanx. The palmar surface of the shaft presents on each side an impressionSfor the tendon of the flexor digitorum sublimis, and the dorsal aspect of the base is marked by a projection for the insertion of the extensor digitorum communis.

Third phalanx

A third phalanx is readily recognised by its small size. The proximal end is identical in shape with that of a second phalanx, and bears a depression in front for the tendon of the flexor digitorum profundus. The free, flattened and expanded distal extremity presents on its palmar surface a rough semilunar elevation for the support of the pulp of the finger. The somewhat horseshoe-shaped free extremity is known as the ungual tuberosity [tuberositas unguicularis], and the bone is accordingly referred to as the ungual phalanx.

Ossification of the Metacarpus and Phalanges

Each of the metacarpal bones and phalanges is ossified from a primary center for the greater part of the bone, and from one epiphysial center. The primary nucleus appears from the eighth to the tenth week of intra-uterine life. In four metacarpal bones the epiphysis is distal, whilst

Ossification of the Metacarpals and Phalanges.

in the first metacarpal bone, and in all the phalanges, it is proximal. The epiphysial nuclei appear from the third to the fifth year and are united to their respective shafts about the twentieth year. In many cases the first metacarpal has two epiphyses, one for the base in the third year and an additional one for the head in the seventh year, but the latter is never so large as in the other metacarpal bones. The third metacarpal occasionally has an additional nucleus for the prominent styloid process which may remain distinct and form a styloid bone, and traces of a proximal epiphysis have been observed in the second metacarpal bone. In many of the Cetacea (whales, dolphins, and porpoises) and in the seal, epiphyses are found at both ends of the metacarpal bones and phalanges (Flower).

The ossification of a terminal phalanx is peculiar. Like the other phalanges, it has a primary nucleus and a secondary nucleus for an epiphysis. But whereas in other phalanges the primary center appears in the middle of the shaft, in the case of the distal phalanges the earthy matter is deposited in the free extremity.

Sesamoid Bones

The sesamoid bones are small and rounded and occur imbedded in certain tendons where they exert a considerable amount of pressure on subjacent bony structures. In the hand five sesamoid bones are of almost constant occurrence, namely, two over the metacarpo-phalangeal joint of the thumb in the tendons of the flexor pollicis brevis, one over the interphalangeal joint of the thumb, and one over the metacarpo-phalangeal joints of the second and fifth fingers. Occasionally sesamoids occur over the metacarpo-phalangeal joint of the third and fourth digits, and an additional one may occur over that of the fifth. Very rarely a sesamoid is developed in the tendon of the biceps over the tuberosity of the radius.