PORE-ARM 



49 



The fore-arm is also supported by a single bone, the radio- 

 ulna (Fig. 8, RA. UL); Its proximal end is concave and 

 articulates with the almost globular condyle of the humerus : 

 the outer or posterior edge of the concavity is produced into 

 a short process, the olecranon or elbow. The distal end is 



cl 



Fig. 13. — Longitudinal sections of the principal long bones of the Frog. 

 A, humerus ; B, radio-ulna ; C, femur ; D, tibio-fibula. en. condyle ; /. foramen 

 for artery ; fi. fibula ; hd. bead ; w.marrow ; ol. olecranon process ; /. bony par- 

 tition ; ra. radius ; sh, shaft ; it, tibia ; »/. ulna. 



incompletely divided into two articular surfaces, and between 

 these is a groove passing for some distance towards the 

 proximal end of the bone. A section shows that at this end 

 there are two distinct marrow-cavities, indicating that the bone 

 is really double. That this is the case is proved by the 



Pract. Zool. E 



