THE METACARPUS 201 



surface is triangular and rough, for ligamentous attachment. The anterior or 

 palmar surface presents, at its lower and inner side, a curved, hook-like process of 

 bone, the unciform process (hamulus ossis hamat'i), directed from the palmar sur- 

 face forward and outward. It gives attachment by its apex to the annular ligament 

 and insertion to the Flexor carpi ulnaris; by its inner surface it gives origin to 

 the Flexor brevis minimi digiti and the Opponens minimi digiti; and is grooved 

 on its outer side, for the passage of the Flexor tendons into the palm of the hand. 

 This is one of the four eminences on the front of the carpus to which the anterior 

 annular ligament is attached, the others being the pisiform internally, the oblique 

 ridge of the trapezium and the tuberosity of the scaphoid externally. The internal 

 surface articulates with the cuneiform by an oblong facet cut obliquely from above, 

 downward and inward. The external surface articulates with the os magnum by 

 its upper and posterior part, the remaining portion being rough, for the attach- 

 ment of ligaments. 



To ascertain to which hand it belongs, hold the apex of the bone upward, and the broad dorsal 

 surface backward; the concavity of the process will be on the side to which the bone belongs. 



Articulations. With five bones the serailunar above, the fourth and fifth metacarpal 

 below, the cuneiform internally, the os magnum externally. 



Attachment of Muscles. To three the Flexor brevis minimi digiti, the Opponens 

 minimi digiti, the Flexor carpi ulnaris. 



The Metacarpus (Ossa Metacarpalia) (Figs. 150, 151). 



The metacarpal bones are five in number, and they are numbered from 1 to 5 

 inclusive, the first being the metacarpal bone of the thumb, the fifth the meta- 

 carpal bone of the little finger. They are long, cylindrical bones, presenting for 

 examination a shaft and two extremities. 



Common Characters of the Metacarpal Bones. The shaft (corpus) is pris- 

 moid in form, and curved longitudinally, so as to be convex in the longitudinal 

 direction behind, concave in front. It presents three surfaces two lateral and 

 one posterior. The two lateral surfaces constitute the palmar or volar aspect. 

 The lateral surfaces are concave, for the origin of the Interossei muscles, and 

 separated from one another by a prominent anterior ridge. The posterior or 

 dorsal surface presents in its distal half a smooth, triangular, flattened area which 

 is covered, in the recent state, by the tendons of the Extensor muscles. This 

 triangular surface is bounded by two lines, which commence in small tubercles 

 situated on the dorsal aspect on either side of the digital extremity, and, running 

 backward, converge to meet some distance behind the centre of the bone and 

 form a ridge which runs along the rest of the dorsal surface to the carpal ex- 

 tremity. This ridge separates two lateral, sloping surfaces for the origin of the 

 Dorsal interossei muscles. 1 To the tubercles on the digital extremities are 

 attached the lateral ligaments of the metacarpophalangeal joints. On the pal- 

 mar surface of each metacarpal bone is a nutrient foramen, which opens into a 

 nutrient canal. In the first metacarpal the direction of this foramen is toward the 

 phalanges (distad). In each of the other metacarpals it is from the phalanges 

 (proximad). 



The carpal or proximal extremity or base (basis) is of a cuboidal form, and broader 

 behind than in front; it articulates above with the carpus, and on each side with 

 the adjoining metacarpal bones; its dorsal and palmar surfaces are rough, for the 

 attachment of tendons and ligaments. 



The distal extremity, or head (capitulum), presents an oblong surface, markedly 



1 By these sloping surfaces the metacarpal bones of the hand may be at once differentiated from the meta- 

 tarsal bones of the foot. 



