FORWARD LOCOMOTIVE ORGANS COMPARED. 41 



members in each case, however, being modified according 

 to the function to be performed, whether it be that of 

 standing, or grasping, or walking, or running, or leaping, 

 or springing, or flying, or creeping, or swimming ; but the 

 general plan is always the same. Figs. 24 and 26, where 

 corresponding parts are marked by the same letter or let- 

 ters, show how the skeleton of Man and the skeleton of 

 a Bird, correspond to one another ; and Figs. 42-52, 

 which exhibit the form of the bones of the forward 

 locomotive members of several kinds of Vertebrates, 

 show clearly that the arm of Man, the arm of the Mon- 

 key, the wing of the Bat, the leg of the Mole, the leg of 

 the Dog, the paddle of the Seal, the leg of the Sheep, 

 the paddle of the Whale, the wing of the Bird, the leg of 

 the Turtle, and the fin of the Fish, are but different expres- 

 sions of one and the same fundamental idea. In the figure 

 of each one of these members, h stands for humerus ; ru, 

 for radius and ulna ; c, for carpus ; me, for metacarpus ; 

 and ph, for phalanges or bones of the fingers. 



PRINCIPAL TOPICS CONSIDERED IN CHAPTER II., SECTION I. 



The Vertebrates defined. Skeleton. Vertebra 1 . Cerebro-spinal system. 



Spinal cavity or neural canal. Hsemal cavity. All vertebrates constructed on 



one plan. Bones; their structure, and composition. Difference between bones 



and shells. Origin of the vertebrate skeleton. Chorda-dorsalis. Jaws of the 



Vertebrates. Teeth cement, dentine, and enamel. Arrangement of the organs 



of the Vertebrates. The blood of Vertebrates. Forms and sizes of the blood 



corpuscles. Structure of the colorless corpuscles. 



Relative size of the Vertebrates. Classification of the Vertebrates as regards 



Classes. Parts of the skeleton in the different classes of tne Vertebrates com- 

 pared. 



