THE SKELETON AND MUSCLES 333 



The parietals (P) lie above the temporals and meet on the 

 top of the head. The frontal bone (F) covers the front 

 part of the brain and forms part of the bony socket that 

 protects the eye. The facial bones are those forming the 

 jaws, the sides of the nose and the roof of the mouth. 



Support of the skull. — The first spinal vertebra, the atlas, 

 supports the skull. This bone articulates movably with the 

 second vertebra called the axis, and permits of much move- 

 ment, as nodding, turning the head, etc. 



Pelvic and pectoral girdlies. — The large pelvic bone (fig. 

 166 A-s) forms the pelvic girdle and contains the socket of 

 the hip-joint (fig. 171), by means of which the legs are ar- 

 ticulated with the axial skeleton. 



The collar bones (clavicles) (fig. 159 C) and shoulder 

 blades (scapulas) (fig. 159 S) form the pectoral girdle. The 

 collar bones, one on either side, may be felt just beneath the 

 neck. They articulate with the sternum in front and at 

 their outer extremities with the upper bone of the arm. The 

 two large shoulder blades at the back, the scapulas, are held 

 in place merely by muscles attached to the ribs. At their 

 outer ends they also articulate with the humerus. The pec- 

 toral girdle articulates with the axial skeleton through the 

 clavicles only. This adjustment permits a wide range of 

 motion to the arms. 



Structure of a long bone. — A bone in a prepared skeleton, 

 or one picked up in the field after it has been exposed to 

 the weather for a long time, shows only the mineral matter 

 of which it is composed. It has lost all of its organic or 

 living material. A fresh bone, procured from the butcher, 

 shows the features indicated in fig. 169. At each end is 

 an enlargement or head, with certain protuberances for the 

 attachment of muscles. The ends are capped with dense 

 white elastic tissue or cartilage (fig. ijod). These are the 

 surfaces that articulate with other bones. The central shaft 

 (fig. 169, x-z) is covered with a sheath of connective tissue. 



