Ti'of. 0. C. Marsh—The Wings of Pterodadyles. 209 



forms in Europe. Beside these, there is often found on the radial 

 side of the wrist, and sometimes attached to it, a long, slender 

 styloid bone, having a rounded articular head on its carpal extremity. 

 This is the so-called " pteroid bone," to which allusion has already 

 been made above. This bone and the "lateral carpal" which 

 supports it are usually placed by anatomists on the outer or ulnar 

 side, but American specimens prove conclusively that they belong 

 on the radial side. 



The nature of the so-called pteroid bone has been much discussed, 

 but without a satisfactory conclusion. After a careful study of many 

 specimens, the writer is disposed to regard it, not as an ossified 

 tendon, but as a part of the first digit, or thumb, which is often con- 

 sidered wanting in Pterodactyles. According to this view, the 

 " lateral carpal " would probably be the metacarpal of the same 

 digit. In favour of this interpretation, it may be said : — 



1. That the position and structure of this appendage of the carpus 

 correspond closely with that of the first digit in some other reptiles, 

 for example, Iguanodon. 



2. The " lateral carpal " unites both with the distal carpal and 

 with the "pteroid " by very free, well-defined articulations. 



3. In American specimens, the " lateral carpal " stands nearly at 

 right angles to the wrist, and the " pteroid " is much bent near its 

 articular end. 



4. In no Pterodactyle known is there any remnant of a digit out- 

 side the wing finger, Avhere the membrane might be expected to 

 retain it. 



5. This view would make the wing finger the fifth digit, the same 

 to which the membrane is attached in the hind foot. 



Perhaps the strongest objection against this interpretation is the 

 number of phalanges in the respective digits of the hand. These, 

 however, are not constant in the known Pterodactyles, and they 

 vary much in other reptiles which have the digits highly specialized. 

 This subject will be more fully discussed by the writer elsewhere. 



According to the above interpi'etation, there are five digits in the 

 hand of Pterodactyles, although not the five often given in restora- 

 tions. The first digit, the elements of which have been considered, 

 undoubtedly supported a membrane in front of the arm. The 

 second, third, and fourth are small, and armed with claws. The 

 large wing finger is the fifth, corresponding to the little finger of 

 the human hand. 



The metacarpal bones are much elongated in the Pterodactyles 

 with short tails, and quite short in those, like the present specimen, 

 that have the tail long. The metacarpal of the wing finger is 

 always large, and robust, while those of the claw-bearing digits are 

 usually quite slender. In Pteranodon, the second metacarpal is a 

 slender thread of bone, throughout most of the length, while the 

 third and fourth are attenuated splint bones, incomplete above. 



The phalanges of the three middle digits are quite short, and the 

 terminal ones supported sharp claws. The wing finger has four 

 greatly elongated phalanges, the last being a styloid bone, without a 



DECADE II. — VOL. IX. NO. V. 14 



