BONES OF THE FORE-LIMB 485 



Its head presents a large double surface for articulatipn 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 ubia. Near the proximal end of the 

 last-mentioned bone is a cavity for the articulation of the 

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

 duced to form a large olecranon process, which is received 

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

 its small distal end articulates with the carpus. 



The carpus consists of a proximal and a distal row of 

 small, nodular bones, which articulate with one another 

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

 beginning at the inner (preaxial) side, are the radiale and 

 intermedium, articulating with the radius, and the ulnare, 

 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 centrale, the others constituting a row of distal carpals. 

 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. pisifortn, 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 metacarpal 3X^6. phalanges, articulating with one another. 

 The innermost (preaxial) digit — the thumb ox pollex — is the 

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

 phalanges, the others three each, the distal or tmgual 

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



