WEALDEN DINOSAURS. 505 



bone, to beyond the middle of the shaft, which then becomes rounded, and finally 

 broadens to near the distal expansion of the bone {k, Ic, fig. 1). 



The humeral articular surface (figs. 1 and 2, d, d') is oblong, and extends from above 

 obliquely downward and forward to the strong anterior ridge (e), which, adding to its 

 width, is then continued down to form (at e) part of tlie cavity for the radius. The 

 humeral surface is concave lengthwise, and also, in less degree, transversely; but both 

 ulnar and radial borders become convex in that direction, or are rounded off and thick. 

 The sharpest or best defined border is that which divides the h)wer part of the humeral 

 articular cavity (fig. 3, d',f, ' greater sigmoid' of Anthropotomy) from that {(/) presented to 

 the radius (' lesser sigmoid cavity,' ib.). 



The length of the humeral cavity is 4^ inches; the breadth across the middle 

 2^ inches : the surface {d',f, g, fig. 2) for the head of the radius appears to be directly con- 

 tinued over the well-defined lower part of the border {d,f) of the preceding cavity, directly 

 downward, or with its plane in the longitudinal axis of the bone. This 'lesser sigmoid 

 cavity' is semi-elliptical in shape, about 2 inches 8 lines in longest diameter, 1 inch 3 lines 

 in the opposite direction ; the upper border is straight, the lower one curved. 'J^he exact 

 extent in the direction transversely to the head of the ulna, or in the long axis of the 

 semi-ellipse, has suffered by fracture of the antero-inferior end or angle of the combined 

 humero-articular cavities. 



About half an inch below the radial surface the ridge (e, fig. 1), continued downward 

 from the above broken angle, expands to a rough tuberosity, which was joined by syndes- 

 mosis to a similar rough tuberosity {r, fig. 3) at the lower part of the anterior articular 

 ridge of the radius. 



At the proximal end of the ulna a thick, rough, long tuberosity, or tuberous ridge 

 (fig. 2, h, h), from the radial side of the huniero-radial articulation, is most prominent 

 where it bounds or defines the radial division of that joint ; below which it contracts and 

 sHghtly bends to its termination (//'). This projection augments the breadth of the back 

 part of the ulna below the base of the olecranon. At this part the ulna is almost flat, 

 and the surface is roughened by thick irregular ridges, which mostly affect a longitudinal 

 direction. 



The general form of the bone at its upper three fourths is three-sided. The hinder 

 side, continued from the above flat, rough expanse, maintains its character of flatness, 

 gradually contracting to its termination 4^ inches above the distal end, where the shaft 

 begins to l)e rounded. 



The ulnar surface of the olecranon is moderately convex, lengthwise and across, for 

 3J inches, or to below the middle of the humeral cavity. Then the surface begins rapidly 

 to expand, by the development of the ulnar boundary (c) of the articulation for the radius, 

 gaining a breadth of 4^ inches. The ulnar surface is here (fig. 1, i) moderately concave, 

 both lengthwise and aci'oss ; half way down the bone the concavity is changed to a sur- 

 face flattened lengthwise, and moderately convex transversely. 



