Prof. 0. C. Marsh— The Wings of Pterodactijles. 207 



The membrane evidently extended from the hind foot to near the 

 base of the tail, but the exact outline of this portion cannot at pre- 

 sent be determined. It was probably not far from the position 

 assigned it in the restoration attempted in the cut given below, 

 Figure 3. The attachment of the inner margin of the membrane to 

 the body was doubtless similar to that seen in bats and flying 

 squirrels. 



In front of the arm, there was likewise a fold of the skin extend- 

 ing probably from near the shoulder to the wrist, as indicated in 

 Figure 3. This fold inclosed a peculiar bone (pteroid), the nature 

 and function of which will be discussed below in considering the 

 osteology of this part of the skeleton. 



The Caudal Membrane. 



The greater portion of the tail of this specimen was free, and 

 without volant attachments. The distal extremity, however, in- 

 cluding the last sixteen short vertebrae, supported a vertical mem- 

 brane, which is shown in Figure 1 (a), and also in Figure 2. This 

 peculiar caudal appendage was of somewhat greater thickness than 

 the patagial membrane of the wings. It was rhomboid in outline, 

 and its upper and lower 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 representing 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. 



Fig. 2. — Caudal extremity of Rhamphorhynehus phyllurus, Marsh ; natural 

 size. Seen from the left side. 



The Scapular Arch. 



The osteology of the scapular arch and Avings of Pterodactyles 

 involves many interesting points, some of which have been discussed 

 by anatomists from Cuvier to those of the present day, but with little 

 agreement of opinion. The cause of this diversity of opinion is 

 mainly due to the fact that the specimens examined have been either 

 too small or too imperfect for accurate determination of their more 

 obscure parts. Fortunately, the museum of Yale College has among 

 its specimens of Cretaceous Pterodactyles (some 600 in all), quite a 

 number with the scapular arch and wing-bones neai'ly perfect, and 

 in position. These specimens were nearly all of gigantic size, 



