O. C. Marsh—The Wings of Pterodactyles. 253 
portions were slightly unequal in form and size. The upper part 
was kept in position by a series of spines, sent off one from near 
the middle of each vertebral centrum, and thus clearly repre- 
senting neural spines. The lower half also was strengthened 
by similar spines, which descended from near the junction of 
the vertebree, and hence were homologous with chevron bones. 
These spines were cartilaginous, and flexible, but sufficiently 
firm in texture to keep the membrane in an upright position. 
FiguRE 1.—Caudal extremity of Rhkamphorhynchus phyllurus, Marsh; 
natural size. Seen from the left side. 
THE Scaputar ARrcH. 
dontia. Probably their great size induced special modifications 
of the scapular arch, which is here far more complicated than 
_ In any other members of the group. 
Y as 
_ ¢lavicles have yet been found. The sternum here shows no 
distinct facets for sternal ribs. 
in the Cretaceous genus Péeranodon, and probably also in 
Some of the other gigantic forms from deposits of this age, the 
