76 A COURSE ON ZOOLOGY. 



tions, and so possess a very considerable freedom of 

 motion. 



The sternum is a flat bone, shaped like a dagger, in the 

 front of the thorax and in the median line. It is con- 

 nected with the ribs, and also with the collar-bones or 

 clavicles, to which it affords a central support. 



The iliac bones are large flat bones ; they are articu- 

 lated together in front, and with the sacrum behind, arid 

 they form the floor of the trunk. 



The upper and lower limbs are very analogous in the 

 number and arrangement of the bony pieces that com- 

 pose them. The hand corresponds exactly to the foot, 

 the forearm to the leg, the arm to the thigh, the shoul- 

 der to the pelvis, which latter may be considered ana- 

 tomically as forming part of the lower limbs. While 

 there are certain differences in form and in the apparent 

 number of corresponding bones in the upper and lower 

 limbs, these differences are due to the difference in func- 

 tion. 



The upper limb includes the shoulder, the arm, the 

 forearm, and the hand. 



The bones of the shoulder are a large flat bone fitting 

 close to the back, and called the scapula or shoulder- 

 blade, and the clavicle, or collar-bone, forming a sort 

 of bow in front, and articulated with the sternum and 

 the scapula. This bone is frequently broken by falls, 

 but its fracture is repaired with great facility. 



The arm contains but one bone, the humerus. This is 

 articulated with the scapula in such a manner that it 

 possesses a freedom of motion so great as to allow it to 

 make a complete rotation on its axis. 



The forearm is composed of two bones, the radius, 

 towards the outside, and the ulna, on the inside. The 



