148 ZOOTOMY. 



pre-axial border of the humerus is external, and in the fore- 

 arm, the distal end is rotated in such a way that while the 

 pre-axial border looks forwards and outwards at the 

 proximal end of the fore-arm, it looks directly inwards at 

 its distal end : the manus, being rotated with the fore-arm, 

 has its pre-axial border inwards. 



92. The humerus, an elongated bone, consisting of a 

 shaft of true bone and of proximal and distal extremities or 

 epiphyses of calcined cartilage. Its proximal end or 

 head is rounded, and articulates with the glenoid cavity : 

 on the pre-axial or radial border the shaft is produced into 

 a large process, the radial tuberosity, on its post-axial 

 or ulnar border into a smaller ulnar tuberosity, the latter 

 being partly formed by the proximal epiphysis. At the distal 

 end of the humerus is the pulley-like trochlea, divided 

 into a smaller radial and a larger ulnar articular surface : the 

 distal end of the shaft has its pre-axial border produced into 

 the external or radial condyle, its post-axial border into 

 the internal or ulnar condyle, both processes im- 

 mediately proximal to the trochlea. 



93. The radius, a slender bone consisting of an ossified 

 shaft and of two calcified epiphyses : the proximal end or 

 head is disc-shaped and slightly excavated for articulation 

 with the humerus, the distal extremity is wide from side to 

 side, concave for articulation with the carpus, and produced 

 pre-axially into the radial styloid process. 



94. The ulna, also formed of shaft and epiphyses ; its 

 proximal end is produced into 'a blunt upwardly-directed 

 process, the olecranon, which, along with the actual 

 proximal end of the bone, furnishes the concave sigmoid 

 cavity, or articular surface working over the trochlea of the 

 humerus. The distal end of the ulna is convex and 

 articulates with the carpus. 



