THE CAEPUS. 



219 



NAVICULAB 



LESSER MULTANGULAR 



GREATER MULTANGULAR 



OS TRIQUETRUM 

 PISIFORM 



OS HAMATUM 



V. METACARPAL 



I. META- 

 CARPAL 



FIRST 



hollowed from before backwards, is divided into two articular areas, of which 

 the lateral is the larger; this is for the head of the capitate bone; the medial, 

 narrow from side to side, articulates with the os hamatum. Its lateral surface, 

 crescentic in shape, serves for articulation with the navicular, and also for the 

 attachment of the interosseous ligaments which connect it with that bone. Its 

 medial surface, of quadrilateral form, is cartilage -covered for articulation with the 

 os triquetrum, and the edge which separates this from the proximal surface has 

 attached to it the interosseous ligament which unites these two bones. The 

 rough dorsal non-articular surface is much smaller than the volar ; by this 

 means the volar and dorsal sur- o s CAPIT 



faces of the bone can readily be os LUN 



determined. The os lunatum 

 articulates with five bones the 

 navicular, the radius, the os 

 triquetrum, the os hamatum, 

 and the capitate bone. 



Os Triquetrum (0 . T. Cunei- 

 form). This bone may be 

 recognised by the small oval 

 or circular facet on its volar 

 surface for the pisiform. This 

 is placed towards the distal part 

 of the volar surface, which 

 is elsewhere rough for liga- 

 ments. The bone is placed 

 obliquely, so that its surfaces 

 cannot be accurately described 

 as distal, proximal, etc. ; but for 

 convenience of description, the PHALANX 

 method already adopted is ad- 

 hered to. The proximal surface 

 has a convex rhombic area 

 for articulation with the distal 

 surface of the articular disc 

 in adduction of the hand, 

 though ordinarily it does not 

 appear to be in contact with 

 that structure. To the medial 

 side of this it is rough for liga- 

 ments. The distal surface is 

 elongated and concavo-convex 

 from radial to ulnar side ; here 

 the bone articulates with the os 

 hamatum. The lateral surface, 

 broader in front than behind, 

 articulates with the os lunatum. 

 The medial surface, rounded and 

 rough, is confluent proximally 

 and dorsally with the proximal 

 and dorsal aspects of the bone. The dorsal surface, rounded and smooth laterally, 

 is ridged and grooved medially for the attachment of ligaments. The os triquetrum 

 articulates with three bones, viz., the pisiform, the os hamatum, and the os lunatum. 

 Os Pisiforme. About the size and shape of a large pea, the pisiform bone 

 rests on the volar surface of the os triquetrum, with which it articulates by 

 an oval or circular facet on its dorsal aspect. The rounded mass of the rest of 

 the bone is non-articular, and inclines distally and laterally so as to overhang 

 the articular facet in front and laterally. The mass of the bone is usually 

 separated from the articular surface by a small but distinct groove. Into the 

 summit of the bone the tendon of the flexor carpi ulnaris muscle is inserted, and 



FIG. 212. THE BONES OF THE RIGHT WRIST AND HAND 



SEEN FROM THE DORSAD ASPECT. 



