396 MR. R. >v. H00LE5T OX XHE [JuilG I913,- 



articular facets looking 'dorsad and laterad' on an anteriorly- 

 directed styliform process were certainly not adapted for this 

 purpose, unless crushing has altered their position and extent. 



The elbow comprised a compact hinge-joint, with perfect rigidity 

 while the limb was used in flight, and, when necessary, complete- 

 flexibility. The strong buttress of bone formed by the doubling- 

 over of the dorsal border of the distal articular extremity of the 

 humerus seems to have originated through the great stress here 

 during flight. The oblique ridge-like epiphysis on the proximal 

 articulatory surface of the ulna articulated in the valley below 

 the buttress, its dorsal face rested and was held under the ventral 

 wall of the buttress, protecting the joint from upward dislocation.. 

 The claw-like postaxial condyle of the humerus, placed against 

 the facet on the postaxial side of the ulna, prevented outward dis- 

 placement, and the V-shaped ridge on the preaxial moiety of the- 

 articular surface of the humerus precluded inward shifting. Any 

 upward, outward, or inward thrust at the elbow would not under 

 ordinary usage disturb the joint. No rotating movement of the 

 elbow was possible. Although the radius decussates the ulna no- 

 pronation or supination such as occurs in man was possible, for . 

 the human radius crosses in an anterior, while that of Ornitho- 

 desmics does so in a posterior direction ; neither does the radius 

 cross so far that its distal end reaches the opposite side as in man,, 

 nor is any rotatory motion possible, for it articulated with the 

 proximal carpal in a deep transverse groove. Moreover, its flat- 

 ventral surface rested upon a similar surface on the dorsal side of 

 the ulna. Such a flexibility would weaken, not strengthen the- 

 wing for flight. This decussation afforded a strut or support in the 

 downward flap of the immense wings. 



The folding of the wing was performed by the help of the three 

 joints of the wrist and that of the wing -metacarpal with the 

 proximal phalange. By the particular form of the ulnar articulation 

 with the proximal carpal, the first joint had the power not only of 

 a hinge-like motion dorso-ventrally, but also of a peculiar turn 

 in a downward and backward direction. This was achieved by 

 aid of the pit-and-ball articulation, and by the articulation of the 

 postaxial articular surface of the ulna, on the ventral surface of 

 that bone, with the raised ventral border of the proximal carpal. 

 At the median joint (a trochlea) of the wrist the only movement 

 possible was pre-postaxial, and thus the reverse of that of the 

 elbow which was dorso-ventral. At the distal carpal and wing- 

 metacarpal joint a rotatory motion was possible. On a turning 

 and bending-back of the wing the two additional articular surfaces 

 on these bones came into union, and continued the bend originated 

 by the proximal joint of the wrist, in such a way that the carpus 

 formed a sort of elbow enabling the wing-metacarpal and phalanges 

 to take an upward position. By the aid of the distal wing- 

 metacarpal and proximal phalange pulley-articulation, the distal 

 portion of the wing could be carried at any inclination in a pre- 

 postaxial arc. The arrangement of the first: and second joints. 



