52 THE HISTORY OF THE PELYCOSAURIA, WITH 



and ends below by recurving sbarply to the shaft. The lower end does not lose itself 

 entirely on the shaft, but remains as a low ridge running down and inwardly to form part 

 of the bridge over the entepicondylar foramen. 



The distal end is expanded at nearly a right angle to the proximal end. The ulnar 

 condyle is rounded, smaller than the radial, and somewhat diagonally placed on the outer 

 extremity of the distal end. The face is unequally divided into two facets by a low 

 ridge. There is no deep anconeal pit on the posterior face of the bone. The radial con- 

 dyle, largely on the anterior face of the bone, is divided into a prominent, rounded exter- 

 nal portion and an inner saddle-shaped portion. The inner portion bears no articular 

 face, but is prominent and rugose. The entepicondylar foramen is situated near the 

 upper part of this inner expansion and is enclosed by a strong bridge, the extension of 

 the ridge upon the shaft of the bone. Above the ulnar condyle a deejD notch represents 

 the ectepicondylar foramen. 



Measurements. 



M. 



Total length 181 



Greatest breadth at distal end 117 



Greatest breadth at proximal end : 096 



Diameter of shaft at centre 024 



Projection of deltoid ridge 035 



The ulna (PI. Ill, Figs. 34, 35) is a slender bone, somewhat longer than the 

 humerus, with a flattened shaft. The shaft becomes gradually smaller toward the distal 

 end and then expands slightly again. The proximal end is excavated on its anterior 

 -face by a deep fossa looking, in the natural position of the bone, upwards as well as for- 

 wards. This cavity is divided by a low ridge into two facets, the larger looking forwards 

 and the smaller and external one looking slightly outwards. This cavity is carried onto 

 the upper face of the bone and divides the inner and outer portions of the proximal end. 

 These extremities are produced above the articular face and form the olecranon process. 

 The outer is the largest and curves inwards, presenting a convex, rugose surface. The 

 distal end of the bone is divided into two distinct articular faces. 



Measurements. 



M. 



Total length I 202 



Greatest breadth at distal end 037 



Greatest breadth at proximal end 055 



The radius (PL III, Fig. 33) is curved and shorter than the ulna. The shaft is 

 lenticular in section with the edges becoming sharp and prominent toward the distal end. 

 The proximal end is expanded and the articular face for the humerus is deeply concave 



