100 MR. H. Q. SEELET ON THE 



other animals in which the metacarpus is unusually modified. One 

 of the two other bones terminates at the end in a rounded articular 

 edge, which gives attachment to another bone, which for conveni- 

 ence may be named the lateral carpal ; it is evidently homologous 

 with the lateral carpal bone of birds, which is probably the pisi- 

 form bone. I am aware that Dr. Foster and Mr. Balfour regard 

 that bone in birds as the united lunar and cuneiform bones. 

 Whichever nomenclature should be preferred, all are agreed that 

 it is attached to the exterior side of the^ distal carpal ; and as it has 

 the same articulation in OrnitJiocheirus^ it follows that the element 

 of the Ornithosaurian distal carpal to which it is attached is the 

 unciform bone ; and to this bone the minutest metacarpal bone is 

 attached (PI. XI. fig. 10) . The other carpal element is therefore the 

 trapezoid ; and that bone will be seen to give attachment to the 

 wing metacarpal bone. The structure of this carpal row, and the 

 articular surfaces on its distal face, demonstrate that the great 

 wing-finger of Ornithosaurs is not the fifth digit, or little finger, as 

 stated by the older writers, but the middle finger, or index finger, 

 as I first determined many years ago. This is a point of some 

 importance, since it removes the Ornithosaurian hand from the 

 category of osteological anomalies, and shows that it is constructed 

 on a plan absolutely identical with the plan of the hand in birds ; 

 for it is the second or index digit in birds also which is chiefly 

 extended for the support of the wing-membrane. 



The distal carpal row of OrnitliocJieirus appears to diff'er from 

 the corresponding bones in birds in being formed from three centres 

 instead of two, though the rule is not constant for all Ornitho- 

 saurs ; while, on the other band, we have no evidence that the two 

 distal carpal cartilages, detected by Dr. Eosenberg, characterize 

 the distal carpal row of all birds. In any case we are justified in cor- 

 relating the two carpal cartilages of the young bird with the exist- 

 ence of the two metacarpal bones of the adult which are anchylosed 

 to them; while, since Pterodactyles have three or four metacarpal 

 bones fully developed, we may expect to find a correspondingnumber 

 of carpal elements in the distal row of the Ornithosaurian carpus. 



I prefer to regard the lateral carpal as the pisiform bone, because 

 it articulates proximally with a third bone of the forearm, which 

 becomes intelligible as the distal end of the olecranon — an inter- 

 pretation to which I am led by a study of certain Ichthyosaurs, 

 regarding the olecranon as a third bone of the forearm, external 

 in position to the ulna, and capable of being developed either 



