3i8 POPULAR SCIENCE MONTHLY. 



But it was in the fore limbs and their attachments that the re- 

 markable adaptation for flight of these animals is found. The 

 shoulder-blade and coracoid, functionally replacing the collar-bone 

 of many animals, were fused together into a stout curved bone, 

 articulating in front with the broad breast-bone and behind with the 

 spines of several fused back-bones or vertebrae. These two shoulder 

 bones thus formed a complete, stout ring, firmly attached in front and 

 behind. Such a mode of articulation of these bones is found in no 

 other animal. To add further to the strength and rigidity of the 

 thorax, the strong upper ribs were not movably articulated, but coossified 

 with the vertebrae. Altogether, the large and broad breast-bone, the 

 complete shoulder-ring, the rigidly fixed u^per ribs and the immov- 

 able vertebrae furnished a support for the attachment of the enormous 

 wing and its necessary muscles that has no parallel for strength among 

 other animals. 



Among the higher animals there 

 are three types of structure whereby 

 the fore limbs are modified into 

 organs of flight. In birds, the arm 

 and fore-arm bones are elongated 

 and strengthened; the bones of the 

 wrist are fused together or wanting, 

 while the few bones of the fingers 

 are welded together and made to 

 Wing of Bat. ^^i^ge sideways. In the bat, among 



mammals, all the bones, save those 

 of the wrist, are elongated and slender. The very slender fingers are 

 spread out fan-like laterally to support the membrane which replaces 

 the feathers of the bird. 



In the pterodactyls, the volant surface, as in the bats, was presented 

 by a thin membrane, which extended from the fore limb to the sides of 

 the body. The bones of the arm were strong, with strong projections 

 for the attachment of muscles; those of the wrist were few in number 

 and closely united. The rudimentary first finger, or thumb, consisting 

 of a single slender bone, was turned backward toward the shoulder for 

 the support of the membrane in front of the elbow. The second, third 

 and fourth fingers were entire, but very small and slender, and were 

 provided at their extremities with very sharp and strongly curved 

 claws. While these fingers were flexible and prehensile, their small 

 size and weakness of attachment (they did not articulate with the wrist) 

 suggest that their only use was for clinging. In strange contrast with 

 these small fingers, the fifth digit, that is the one corresponding to the 

 little finger of the human hand, was enormously elongated and strong, 

 including by far the largest bones of the entire skeleton. Between 



