LIMBS OF VERTEBRATES 



237 



the air-breathing vertebrates : ambulatory legs, wings and 

 paddles, employed in totally different methods of locomotion and 

 differing widely from one another in general form and appear- 

 ance. Yet when we come to examine' these organs closely we very 

 soon discover the remarkable fact that all are constructed on 

 essentially the same plan ; all belong to what is known as the 

 pentadactyl or five-fingered type of appendage. 



We ourselves retain this type of limb-structure in a compara- 

 tively primitive condition (Fig. 94), although our fore limbs have 

 taken on new functions as organs of prehension. The fore limb 



FlG. 93. Shoulder Girdle and part of Sternum of Ornithorhynchus, seen 



from below. 



Cl. Clavicle ; Cor. Coraeoid ; Ep. C. Epicoracoid ; Gl. Glenoid cavity ; Int. Interclavicle ; 

 B. Ribs ; Sc. Scapula ; St. Sternum. 



consists of arm, forearm, wrist and hand (manus) with five 

 fingers ; the hind limb of thigh, leg, ankle and foot (pes) with five 

 toes. Each segment of the limb is supported by an internal 

 skeleton of bone which is clothed with muscle and skin. The bones 

 are articulated with one another at the joints and moved like so 

 many levers by the contraction of the muscles attached to them. 

 The bone of the arm is the humerus and the corresponding bone of 

 the thigh is the femur. In the forearm we find the radius and 

 ulna and these are represented in the leg by the tibia and fibula. 

 The wrist is made up of a number of small carpal bones and the 

 ankle of a number of more or less similar tarsals. These small 

 bones are arranged mainly in two rows, and the distal or far row 



