THE SKELETON 



373 



the spinal cord. The surface of the centrum and those parts of 

 the vertebrae each of which fits into its next neighbor are covered 

 with pads of cartilage. Two of the processes in each vertebra 

 project forward and two backward; these form articulations or 

 joints with the neighboring vertebrsB. Of the other processes, 

 one projects dorsally and two project laterally; these give attach- 

 ment to the muscles of the back. The two vertebrae directly be- 

 neath the head are modified so as to permit the skull to rest in the 

 upper one; this articulates freely with the second vertebra, thus 

 permitting of the nodding and turning movements of the head. 

 Besides these individual adaptations, the vertebral column, as a 

 whole, is peculiarly adapted to pro- 

 tect the brain from jar; this is seen 

 in the double bend of the vertebral 

 column and the pads of cartilage be- 

 tween the individual vertebrae. The 

 whole column of vertebrae joined 

 each to the other supports the weight 

 of the body. The largest vertebrae 

 at the base are joined to the huge 

 pelvic bones for the better support 

 of the body above. That part of the 

 vertebral column of man which bears the ribs is known as the 

 thoracic region. The ribs, twelve in number, are long bones 

 which combine lightness with strength; joined by elastic cartilage 

 to the sternum in front and to the vertebrae behind, they form a 

 wonderful protection to the organs in the thoracic cavity and j^et 

 allow free movement in breathing. That part of the skeleton 

 to which the bones of the anterior and posterior appendages are 

 attached are respectively known as the pectoral girdle (from 

 which hangs the arm) and the jpelvic girdle (which joins the leg 

 bones to the axial skeleton). 



The Appendages. — The bones of the appendages attached to 

 the pectoral and pelvic girdles are adapted peculiarly to locomo- 

 tion and support; for this purpose the bones are long and strong, 

 hinged by very flexible joints. The latter are especially free in 

 the hand to allow for grasping. In the leg, where weight must be 



Vertebra, showing attachment of 

 ribs; C, centrum; i2., ribs ; SP., 

 spinous process. 



