ANIMAL BIOLOGY 



Attached by movable joints to the vertebrae of the 

 trunk are the ribs. All but the two lower pairs are joined 

 by cartilage to the flat sternum or breast bone which you 

 can easily feel in the front of the chest. The last or float- 

 ing ribs are free in front, thus permitting a greater expan- 

 sion of the chest cavity. 



Forming a support for the arms are the scapula or 

 shoulder blade, and a narrow bone, the clavicle, which 

 extends from the upper end of the sternum to the scapula 

 near the articulation of the arm. Both these bones give 

 attachment to muscles that move the arm and to certain 

 other muscles of the neck and trunk. The upper bone of 

 the arm, or humerus, is joined to the scapula by a ball- 

 and-socket joint. At the elbow, one of the bones of the 

 fore arm, the ulna, is joined to the humerus by a hinge 

 joint, while the other bone, the radius, which lies on the 

 same side as the thumb is joined to the ulna in such a 

 way as to permit it to rotate about the latter with the 

 greatest freedom. The wrist composed of eight small 

 bones, or carpals, is followed by the five metacarpals in 

 the palm of the hand, and these give attachment to the 

 phalanges of the thumb and fingers. 



The hip bones which give attachment to the lower 

 extremities are united into a solid arch, the pelvis, which is 

 firmly joined to the fused vertebrae forming the sacrum. 

 The large size of the pelvis is necessary for the attachment 

 of the large muscles that move the legs as well as the 

 various muscles of the trunk. There is a close similarity 

 between the bones of the legs and those of the arms. 

 Corresponding to the humerus is the femur, the head of 

 which joins by a ball-and-socket joint to the pelvis. 

 At the knee the tibia and fibula, corresponding respectively 

 to the radius and the ulna, are united by a hinge joint to 

 the femur. The carpals of the wrist are the representa- 



