THE CARPUS. 



313 



or concave. The palmar surface, of about the same shape as the dorsal, presents 

 externally a deep groove, a part of the canal for the flexor tendons, overhung inter- 

 nally by the unciform process, which has a broad outer and inner surface, the former 

 concave and smooth, the latter convex. The free border of the hook presents a 

 curved outline from the inner side. The rounded edge between the proximal and 

 outer surfaces rests against the semilunar. The proximal surface is a spirally 

 twisted, oblong facet corresponding to the adjacent side of the cuneiform, with a 

 prominent convexity at the proximal end. The outer surface, rough at the distal 

 and palmar angles for an interosseous ligament, is elsewhere articular for the os 



Fig. 335. 



For cuneiform 



Fig. 336. 



For fifth 

 metacarpal 



Inner border 



Hook 



For magnum 



For fourth 

 metacarpa 



For fifth 

 metacarpal 



Right unciform, inner and proximal aspect. 



Hook 

 Right unciform, outer and distal aspect. 



magnum. The distal surface, wholly articular, bears the fourth and fifth metacarpals, 

 a ridge marking the interspace between them. The surface is, in the main, convex 

 from side to side and concave from dorsum to palm. Often, however, the part for 

 the fourth finger is concave from side to side and convex in the other direction. 

 The distal surface may meet the proximal at a sharp border, or a very narrow rough 

 surface may intervene. The unciform articulates with five bones, — the semilunar, 

 cuneiform, os magnum, and fourth and fifth metacarpals. 



Development and Variations. — In early foetal life centres appear for the 

 above-described carpal bones, and also for many others, which disappear, or are 

 fused with the usual ones, long before the appearance of bone. Additional carpals 

 depend either on the persistence and subsequent ossification of centres that normally 

 are lost or on the separate development of two or more that should fuse. The 

 number of carpal elements is put by Pfitzner^ at thirty-three. He arranges the 

 constant and possible bones in five rows : (i) an antibrachial row, consisting of an 

 ossification in or on the triangular cartilage, representing the os intermedium, and a 

 little apparent outgrowth from the pisiform ; (2) a proximal roiv, consisting of the 

 normal bones and certain subdivisions of the scaphoid and cuneiform ; (3) a central 

 row, composed entirely of occasional bones ; (4) a distal row, composed of the four 

 normal bones plus a minute metastyloid ; (5) a carpo-vietacarpal row, composed 

 entirely of occasional bones. The most common anomaly is the appearance of a 

 styloid bojie, which is the separated styloid process of the third metacarpal. The 

 metastyloid of the fourth row is a minute bone representing the very tip of the styloid. 

 Very rarelv the scaphoid is divided into a radial and an ulnar part. The os centrale 

 is the persistence of still another piece, which normally either joins the scaphoid in 

 the third month of fcetal life or disappears. It apparendy is composed of a dorsal_ 

 and a palmar element, of which the latter is the more subject to degeneration. The 

 OS magnum contains two elements exceedingly rarely found distinct, the subcapi- 

 latum on the distal end of the palmar surface and the subcapitatum secunda7'ium. 

 forming the inner distal angle of the dorsum. The hook of the unciform may be 

 separate. Fusion may occur between bones normally distinct. The semilunar may 

 fuse with the cuneiform, especially in negroes. 



Ossification occurs from one centre for each bone ; but according to some 

 authorities, the unciform and the scaphoid have two centres. The former and the os 



' Zeitschrift fiir Morphologic und Anthropol., Bd. ii., 1900. 



