60 



THE CERATOPSIA. 



considering the»enormous weight of the skull and its investing musculature. Anterior and 

 posterior views of the humerus are shown here in figs. 65 and 66, while external and internal 

 lateral views of the fore limb may be seen in the restoration of the skeleton in PI. XLIX. 



THE HUMERUS. 



The humerus is greatly expanded at either extremity, but much constricted just below 

 the radial crest, which is exceptionally well developed and extends from the superior 

 extremitj'- down the antero-internal border throughout about two-thirds the length of the bone. 

 The head is situated in about the middle of the proximal end and is produced only a little 

 backward beyond the posterior border of the shaft of the humerus. At the distal end the 

 radial and ulnar condyles are well differentiated and separated by broad and deep trochlea. 



lit. m, 



Fig. 6.5.— Anterior view of right humerus of 

 Triceratops prorsus Marsh, No. 4842, TJ. S. 

 National Museum, in mounted skeleton. 

 One-eighth natural size. 



Fig. 66.— Posterior view of right humerus of Triceratops 

 prorsus Marsh, No. 4S42, TJ. S. National Museum, in 

 mounted skeleton, h, Head; r, radial crest; re, radial 

 condyle; uc, ulnar condyle. One-eighth natural size. 

 After Marsh. 



The anconeal fossa is shallow, scarcely exceeding in depth the cavity situated directly opposite 

 on the anterior face of the humerus. The humerus is proportionally somewhat longer when 

 compared with the femur than are the bones of the fore arm as compared with the tibia and 

 fibula. The general form of the humerus is well shown in figs. 65 and 66. 



THE ULNA. 



The ulna is extremely massive above, but smaller below. There is a slight constriction 

 in the shaft a little above the distal extremity. The olecranon is massive and is produced far 

 above the proximal end of the radius, as in most mammals, conditions differing materially 

 from those which obtain in this element in most dinosaurs. 



