506 



BONES OF THE HAND. 



by this bone is easily felt during life, more 

 especially during flexion of the wrist-joint. 

 It is round every where, except posteriorly, 

 where it presents a flat circular surface, by 

 which it is articulated with the cuneiform bone. 

 This bone is intimately connected with and 

 as it were inclosed in the terminal portion of 

 the tendon of the flexor carpi ulnaris. 



5. Os trapezium (os multangulum majus ; 

 Fr. le trapeze ; Germ, das grosse vielwinkliche 

 Bein). This bone is situated at the radial 

 extremity of the inferior carpal row, having the 

 scaphoid above it and the metacarpal bone of 

 the thumb below it. We may describe six 

 surfaces upon it, four articular and two non- 

 articular. . A large articular surface, situated 

 on the external and inferior aspect of the bone. 

 This surface is for articulation with the meta- 

 carpal bone of the thumb : it is somewhat oval 

 in form, the long axis passing from without 

 inwards and downwards ; in this direction it is 

 concave, from before backwards it is convex. 

 The three remaining articular surfaces are on 

 the internal and superior aspects of the bone. 

 6. Internally, a very small plane surface, 

 adapted to a corresponding one on the radial 

 side of the carpal extremity of the second 

 metacarpal bone. c. Above the last described 

 surface and separated from it merely by a slight 

 ridge, we find one of a somewhat triangular form 

 and slightly concave, articulated with the radial 

 side of the trapezoid. d. Quite on the superior 

 aspect a small semicircular surface, adapted 

 to the scaphoid. Of the non-articular surfaces, 

 one is on the palmar aspect of the bone, and 

 is easily distinguished by the prominent ridge 

 or tubercle at its outer part, which gives attach- 

 ment to the annular ligament, (tuberculum, 

 eminentia carpi radialis inferior ;) and on the 

 ulnar side of this ridge a groove in which the 

 tendon of the flexor carpi radialis glides. The 

 second non-articula*r surface is on the dorsal 

 aspect : it is more extensive than the last, 

 rough and tuberculated, affording insertion to 

 ligaments. 



6. Os trapezoides (os multangulum minus; 

 Fr. le trapezoide; Germ, das Kleine viel- 

 winkliche Bein), This is the second bone of 

 the inferior carpal row ; it has the os trapezium 

 on its radial and the os magnum on its ulnar 

 side, the scaphoid above and the second meta- 

 carpal bone below it. We describe four articular 

 surfaces and two non-articular, a. The inferior 

 one the largest, quadrilateral, much narrower 

 in front than behind, convex from side to side, 

 slightly concave from before backwards, is 

 entirely devoted to articulation with the second 

 metacarpal bone. b. On the radial side, a 

 slightly convex surface for the trapezium. 

 c. Superiorly a quadrilateral concave surface 

 for articulation with the scaphoid, d. On the 

 ulnar side a very small surface, adapted to a 

 corresponding one-, on the radial side of the os 

 magnum. The palmar surface is non-articular, 

 five-sided, slightly excavated, and rough from 

 the insertion of ligaments. The dorsal surface, 

 also non- articular, is of greater extent, con- 

 vex, and likewise rough. 



7. Os nwgnum (os capitatum ; Fr. le grand 



os ; Germ, das Kopfbem). This bone is, as 

 its name implies, principally characterized by 

 its excess in size over the other carpal bones, 

 and from the number of bones with which it is 

 connected, it may be regarded as the key-bone 

 of the carpus. Superiorly it is in the form of 

 a rounded head (capitulum}, flattened on the 

 ulnar side, where it articulates with the unciform 

 bone. The superior prominent portion of this 

 head is received into the excavation of the lunar 

 bone, and by its radial side it articulates with 

 the inferior hollow surface of the scaphoid. 

 The inferior portion of the bone is cuboid, and 

 has been called the body ; it is rough and con- 

 vex on its palmar surface, also rough but 

 irregular on its dorsal, both these surfaces 

 affording insertion to numerous ligaments. 

 Inferiorly we notice an extensive articular sur- 

 face, which is adapted in the centre to the 

 third metacarpal bone, on the radial side to the 

 second, and by a very small portion on the 

 ulnar side to the fourth metacarpal bone. On 

 the ulnar side of its inferior portion it articu- 

 lates a second time with the os unciforme 

 by a small circular articular surface, the cir- 

 cumference of which nearly equals that of the 

 flat surface of a split pea. Lastly, on its radial 

 side it articulates with the trapezoid bone. 

 Thus the os magnum articulates with seven 

 bones; three metacarpal bones, two carpal 

 bones in the inferior row, and two in the supe- 

 rior row. 



8. Os unciforme (from uncus, a hook, os ha- 

 matum ; Fr. 'l'os crochu ou unciforme ; Germ. 

 das Hakenbein, oder Keilformiger Knochen). 

 This bone has received its name from that 

 which allows of its being easily distinguished 

 from all the carpal bones, namely, the hooked 

 process, which projects from the radial edge of 

 its palmar surface. This process constitutes a 

 considerable prominence on the ulnar side of 

 the carpus (eminentia carpi ulnaris inferior), 

 and affords insertion to the annular ligament. 

 Its concavity looks towards the radial side of 

 the carpus ; the remainder of the palmar sur- 

 face is rough for ligamentous insertion. The 

 dorsal surface is likewise rough, convex, and 

 of considerable extent. This bone articulates 

 inferiorly with the fourth and fifth metacarpal 

 bones, on its radial side with the os magnum, and 

 on its superior surface with the cuneiform bone. 



Structure of the carpal bones. These bones 

 are chiefly composed of the reticular osseous 

 tissue, to which their extreme lightness is attri- 

 butable, the surface being invested by a thin 

 layer of compact texture, in this respect per- 

 fectly resembling the bones of the tarsus. 



Developement . The carpal bones are very 

 late in their developement ; at birth they are 

 completely cartilaginous. According to Cru- 

 veilhier, each bone is developed by a single 

 point of ossification. The os magnum and os 

 unciforme are the first in which the ossific pro- 

 cess commences, about the end of the first 

 year; between the third and fourth years it 

 begins in the cuneiform, a year later in the 

 trapezium and lunar, and between the eighth 

 and ninth years in the scaphoid and trapezoid 

 bones. The ossification of the pisiform does 



