THE FORE-LIMB. 423 



by two tuberosities, which are preaxial and 

 postaxial respectively. 



The preaxial tuberosity is small, but is 

 continued along the bone as the prominent 

 forwardly directed deltoid ridge : . this gives 

 insertion to the great pectoral and deltoid 

 muscles ; while a small tubercle at its proxi- 

 mal end, and partly on the extensor surface, 

 marks the insertion of the tendon of the second 

 pectoral muscle, or elevator of the wing. 



The postaxial or greater tuberosity is much 

 larger, and has on its extensor surface a deep 

 pit, the pneumatic foramen, leading to an 

 air-cavity in the shaft of the bone. 



The distal end of the humerus bears a 

 trochlear articular surface for the radius and 

 ulna, the radial surface being preaxial, and 

 placed obliquely to the long axis of the bone ; 

 the ulnar surface being postaxial, and trans- 

 verse to the axis. 



2. The forearm has two bones, which are separate from 

 each other along their whole length, 

 i. The radius is slender and nearly straight. Its 

 proximal end, or head, presents a terminal 

 cup-shaped articular surface for the preaxial 

 condyle of the humerus ; and its distal end 

 articulates with the carpus. 



ii. The ulna is rather longer and much stouter 

 than the radius, and is slightly curved. Its 

 proximal and larger end has a large articular 

 surface for the postaxial tubercle of the 

 humerus, beyond which it projects as the 

 blunt olecranon process. Its distal end articu- 

 lates with the carpus and with the radius. 



3. The wrist consists, in the embryo, of two rows of carpals, 

 a proximal row of two and a distal row of three. Of 



