704 5. W. WILLISTON 



in life than any that has hitherto been published. That the 

 membrane extended on the neck is of course yet a hypothesis 

 based upon the mode of development of the parachute in flying 

 animals of today, and especially upon the structure of the pteroid 

 bone and its relations to the forearm and shoulder. It is a fact 

 that this bone seems to be better developed in Nyctosaurus than 

 in other known pterodactyls, reaching by its pointed extremity 

 pretty well toward the shoulder. If it was divaricated from the 

 arm, as its perfect ball-and-socket mode of articulation with the 

 carpus would indicate, and not inclosed in a muscle at its pointed 

 extremity, its function as a supporter of a membrane in front of the 

 elbow can scarcely be taken into consideration. With the mem- 

 brane extending past the shoulder to the neck it would have had 

 a distinct function as a " Spannknochen " and not otherwise. 



Objection may be raised against the wide expanse of membrane 

 between the legs. That the membrane extended to the tarsus on 

 the peroneal side of the legs I think now hardly admits of doubt; the 

 animals would hardly have been "nugfahig" were the legs wholly 

 free, since the wing membrane would have been too narrow to serve 

 as a parachute, and since the legs with their attached membrane 

 must have functioned much like the tail feathers of modern birds 

 in the control of flight. Rhamphorhynchus gemmingi has been 

 restored by Zittel without membrane between the legs, but such a 

 condition must seem impossible for such a flying creature. With 

 the wings extended and the membrane connected with the ankles, 

 there must have been a constant and considerable abducting strain 

 on the legs, which must have required a constant muscular tension 

 to withstand; and the legs, in the later pterodactyls at least, seem 

 too frail for such tension. The head of mammals in the horizontal 

 position is kept in place, not by muscular action, which would be 

 unbearable, but by the elastic ligament of the neck. Something 

 like this must have been necessary to withstand the constant 

 abducting tension of the legs of pterodactyls in flight, and I assume 

 that this was the function of a tense membrane between the legs, 

 as well as that of directing flight. It has been suggested that the 

 border of this membrane connected with the end of the vestigial 

 tail; possibly that was the case, but, in Nyctosaurus at least, such 



