llAixiir.k: l''oRi; l.i.Mi: and iManu.s oi Bkoxtosaurus. 303 



imperfectly defined external condyle, 

 the humerus is regularly convex 

 transversely throughout most of its 

 length, though much flattened prox- 

 imally and slightly grooved dis- 

 tally. The i)rincipal characters are 

 shown in Figs, i, 2, 3, which pre- 

 sent respectively the anterior, pos- 

 terior, and distal views of this bone. 

 The principal measurements are : 



'i'he i)Osterior border of 



Fig. 3. Distal end of right hu- 

 merus about one- tenth natural size. 

 (No. 563.) 



Greatest length, 1,100 mm. 



" transverse diameter at proximal end, 600 " 



" " " " distal " 410 " 



'Iransver.se diameter at point of greatest constriction, 210 " 



8X •' 



T/ie Radius and Ulna. — These bones are subequal in size. The 

 distal third of the ulna is a little more slender than the same portion 

 of the radius as shown in plates XIX. and XX., and in Figs. 4, 5, 6, 

 7, S, and 9. The shaft of the radius is constricted medially while the 

 ends are about equally exjianded. The proximal end is semi-circular 

 in cross-section, the convex surface fitting nicely into the radial groove 

 on the anterior surface of the proximal end of the ulna. Proximally 

 the radius articulates only with the anterior and internal portion of 

 the distal articular surface of the humerus, as is well shown in Figs. 4 

 and 6 and in plate XX. The proximal end of the ulna entirely en- 

 closes that of the radius posteriorly and externally so that its articular 

 surface is opposed to that of the distal end of the humerus posteriorly 

 throughout its entire breadth, while at the same time presenting a 

 broad and deep articular surface on the anterior projection which en- 

 closes the radius externally for contact with that of the anterior and 

 external surface of the humerus. The contact of the radius with the 

 humerus is thus limited to the antero-internal surface of the humerus 

 instead of the antero-external as determined by Osborn and Granger/ 

 so that these bones are not so completely crossed as these authors had 

 supposed, but occupy positions almost identical with those figured by 

 the late Professor Marsh as obtaining in the fore limb of Morosaurus.^ 

 Seen from above the proximal end of the ulna may best be described 



'See Bui. Am. Mus. Nat. Hist., Vol. XIV., pp. 199-20S. 



«See Part I. Sixteenth An. Report U. S. G. S., pp. I43-244, P'atc X.WVII. 



