. Bulletin. Natural history; Natuurlijke historie. c m FIG. 60. Right carpalia of Deinonychus antirrhopus. Radiale (YPM 5211) in proximal (A), distal (B) and ventral or palmar (C) views. Ulnare (YPM 5228) in proximal (D), distal (E) and ventral or palmar (F) views. Abbreviations: ra—articular facet for radius; ra'—articular "stop" for radius; ul—articular facet for ulna; 1, 2, and 3—articular facets for metacarpals I, II and III. verse, parallel to the plane of metacarpals I and II. Hence this joint facet produced adduction and abduction rather than flexion or extension of the digits
. Bulletin. Natural history; Natuurlijke historie. c m FIG. 60. Right carpalia of Deinonychus antirrhopus. Radiale (YPM 5211) in proximal (A), distal (B) and ventral or palmar (C) views. Ulnare (YPM 5228) in proximal (D), distal (E) and ventral or palmar (F) views. Abbreviations: ra—articular facet for radius; ra'—articular "stop" for radius; ul—articular facet for ulna; 1, 2, and 3—articular facets for metacarpals I, II and III. verse, parallel to the plane of metacarpals I and II. Hence this joint facet produced adduction and abduction rather than flexion or extension of the digits. From a fully pronated position of the manus, with the digits extending for- ward and the forearm in horizontal position in a parasagittal plane, the hand could be adducted approximately 50° and abducted nearly 45° from the para- sagittal plane. During adduction, the manus supinated approximately 45°. Ap- parently little or no pronation occurred at this joint when the carpus was ab- ducted beyond the parasagittal position. In other words, all pronation at the wrist occurred during the first phases of abduction from the fully adducted position. The distal surface of the radiale is divided into two distinct facets separated by a moderate-sized, vertical ridge (Fig. 60B). Both facets are shallow con- cavities, the medial one being subtriangular in shape and the lateral facet quadrangular. The former is the facet for metacarpal I and the latter for metacarpal II. The two metacarpals fit these facets so perfectly and snugly there appears to have been very little mobility between the radiale and either metacarpal. Although there is no co-ossification, I believe that these three elements operated almost as a single unit. Ulnare The ulnare (Fig. 60D-F) is a small, oval-shaped bone, which, like the radiale, appears to have been constant in shape. It is represented by five examples from two of the three Deinonychus sites. On the evidence of YPM 5208 (left radiale and ulnare f
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