WING BONES. 29 



radial crest extended at its full length, but also alters the head of the humerus in such 

 a way that the radial crest appears to originate further from the proximal condyle. 



A practical test of this theory has been obtained by performing the following simple 

 experiments, adapted from Professor Daubree's admirable method of artificial mountain- 

 making : Two models of the humerus were made from soft clay, simulating the original 

 form of the bone as closely as possible. These models were crushed between two flat 

 surfaces, the direction of pressure in one instance being normal to the upper or anconal 

 side, and in the other instance being normal to the radial side of the bone. The result 

 of the first experiment was that the crushed model assumed the form of the humerus 

 of P. occidentalis (type), while the result of the second experiment was that the model 

 assumed the form of the humerus of Pteranodon sp., No. 2302, shown in Plate XX, 

 figures 4 and 5. While these simple ossifragous experiments obviously failed to comply 

 with the exact conditions prevailing in nature, they add considerable weight to the 

 writer's opinion that the different forms of humeri shown in Plate XX are due solely 

 to the varying conditions of pressure to which the bones were subjected. All doubt 

 upon this matter would be removed if the humeri belonging to one individual were 

 found differently crushed ; unfortunately, in not one of the 465 examples of Pteranodon 

 in the collection are the proximal portions of both humeri preserved. 



In Plate XIX, figures 3, 4 a, and 4 b, the left ulna and the ends of the left radius of 

 P. ingens, No. 1175, are shown, the palmar or inferior surface of the ulna being toward 

 the observer. The proximal ends of the radius and ulna and the distal end of the 

 radius, all three fragments belonging to the right wing of No. 1164, type of P. occiden- 

 talis, are shown in Plate XIX, figures 11, 12 a, and 12 b. Some of the bones of the 

 left wing of Pteranodon sp., No. 2425, are figured in Plate XXI, just as they are pre- 

 served in the matrix. The radius and ulna are here practically entire, and appear to 

 have retained their natural positions relative to each other, although their articulations 

 with the humerus and carpus are dislocated. This specimen is also valuable for the 

 excellent state of preservation of the tw> larger carpals, usually distinguished by the 

 terms "proximal" and "distal." A view of the inferior or palmar surface of these 

 bones, on a larger scale, is shown in Plate XXII, figure 1. A small slender bone of 

 doubtful identity occupies the place of the third or lateral carpal in this specimen, but 

 the process for the support of that carpal, arising from the radial side of the distal 

 carpal, is admirably preserved. The reverse side of the slab containing this specimen 

 has been excavated so as to permit Plate XXII, figure 2, to be made, which shows the 

 dorsal side of the carpus. Three views of the left carpus of P. ingens. No. 1175, are 

 given in Plate XIX, figures 6, 7, and 8. In figure 6, showing the proximal surface of 

 the carpus, the distal carpal is nearly concealed, but the greater part of the lateral 

 carpal is visible. Figure 7 is taken from the dorsal view of the carpus, all three bones 

 being compressed in the direction of the axis of the wing. In figure 8, the distal view 

 of the carpus, the outlines of the distal and lateral carpals are clearly seen, the latter 

 borne by a process extending from the radio-palmar angle of the distal carpal. In 

 assembling the carpus for illustration, it was found impossible to maintain a perfect 

 contact between the distal and lateral carpals without rotating the lateral carpal slightly 

 from that position in which it would best support the first metacarpal or " pteroid 

 bone." The carpus of P. occidentalis No. 1164, shown in Plate XIX, figures 13 and 14, 

 appears to be precisely similar to that of P. ingens just described, except that the lateral 

 carpal of P. occidentalis is differently crushed and makes a better contact with the distal 



