38 



TEETIAET VEETEBEATA OF THE EAYtTM. 



lobe is nearly vertical and does not extend so high up as the upper end of the 

 olecranon process. Of the two horizontal surfaces the inner (^.) is much the larger 

 and is oval in outline, its antero-posterior diameter being slightly greater than the 

 transverse ; it is concave in all directions. The outer (o.) is the smaller and is 

 semicircular in outline, the diameter of the semicircle looking forwards and inwards 

 and marking the line of union with the radius, with which the bone unites in a 

 narrow vertical surface {r,s.). Immediately beneath the transverse articulation is 



A\i 



Text-fig. 18. 

 B X? 



r.s. 



Left ulna of Arsinoitherium zitteli : A, from front ; B, from outer side ; C, proximal end (with radius) ; 



D, distal end (with radius). 



CM., surface for cuneiform ; e.p., external prominence ; g., groove above distal articular end ; i., inner surface 

 for humerus ; I., surface for lunar ; o., outer surface for humerus ; ol., olecranon process ; r., radius ; 

 r.s., proximal surface for radius ; r.s,', distal surface for radius ; sc, surface for scaphoid ; u., ulna. 

 ^ nat. size. 



a deep fossa which receives the head of the radius. The shaft of the bone is 

 triangular in section, the posterior angle being continuous with the hinder border 

 of the olecranon process. The shaft is also curved somewhat backwards and 

 inwards. Towards the distal end; which is considerably enlarged, the inner border 



