SKELETON OF VEKTEBRATA. 359 



Tortoise and the Bird, which appear to exhibit the 

 most opposite proportions of these elements : but 

 Cuvier regards this theory as untenable. 



Last in the order of constancy come the bones of 

 the extremities. As we ascend in the scale of ani- 

 mals we may observe the prevalence of a tendency 

 to the concentration of organs, and consequently to 

 the diminution of their number. While in animals of 

 the inferior orders, which are possessed of extremi- 

 ties, we find a considerable number of legs; in all 

 the animals comprised in the class of true insects 

 nature has limited the number to six ; and in the 

 Vertebrata it never exceeds four. As in insects we 

 observed that all the legs are divided into the same 

 number of parts ; so we find among Quadrupeds a 

 striking correspondence in the bones of the fore 

 and the hind extremities. Both the one and the 

 other are connected with the spine by the inter- 

 medium of large and broad bones, which are in- 

 tended to serve as a basis for their more secure 

 attachment, and for giving, at the same time, ex- 

 tensive and advantageous purchase to the muscles, 

 which are to move the limbs. The two bones by 

 which the anterior extremity is connected with the 

 trunk are the blade-hone, or Scapula (b), which sends 

 out a process called the coracoid-bone ; and the 

 collarbone, or the Clavicle,* which extends from the 

 scapula to the sternum. The corresponding con- 



* This bone does not exist in the skeleton of the hog ; but its form 

 and connexions with the sternum and scapula in the human skeleton 

 are shown in Fig. 182, where s is the sternum ; x, the xiphoid car- 

 tilage ; c, the clavicle : b, the scapula ; a, the acromion ; k, the cora- 

 coid process ; and g, the glenoid cavity for the articulation of the 

 humerus. 



