X BONES OF THE FORE-LIMB 485 



Its head presents a large double surface for articulation with 

 the trochlea of the humerus, and its distal extremity a pair 

 of slight concavities for the bones of the carpus ; the shaft 

 is flattened where it abuts against the corresponding flat- 

 tened surface of the ulna. Near the proximal end of the 

 last-mentioned bone is a ca\ity for the articulation of the 

 humerus, and proximally to this, at the elbow, the ulna is pro- 

 duced to form a large olecranon pi-ocess., which is received 

 into the fossa on the humerus when the limb is extended : 

 its small distal end articulates with the carpus. 



'I'he carpus consists of a proximal and a distal row of 

 small, nodular bones, which articulate with one another 

 where the)' are in contact. The bones of the proximal row, 

 beginning at the inner (preaxial) side, are the ?-adiah' and 

 inferinediiim, articulating with the radius, and the i/hiare, 

 articulating with the ulna. In the distal row are five bones, 

 the middle one of which is distinctly proximal to the other 

 four, so as really to lie in the middle of the carpus : this is 

 the cenfrak, the others constituting a row of distal cai-pa/s. 

 Of these the first three articulate with the corresponding 

 digits, the fourth, on the outer (postaxial) side, supporting 

 the fourth and fifth digits, and really consisting of two 

 carpals fused together. A small bone, the pisiform, articu- 

 lating with the ulna and ulnare on the ventral side, is 

 usually looked upon as a sesamoid bone, i.e., an ossification 

 in the tendon of a muscle ; but it may represent the vestige 

 of a sixth digit. 



The hand or manus consists of five digits, each made up 

 of a )netacarpal SlwA phalanges, articulating with one another. 

 The innermost (preaxial) digit — the thumb or polle.x — is the 

 shortest, and the third the longest : the former has two 

 phalanges, the others three each, the distal or ungual 

 phalanx of all the digits having a conical form, its dorsal 



