256 



ADVANCED PHYSIOLOGY 



FIG. 126. TOP OF A 

 BABY'S SKULL 



Showing the bones of the 

 cranium not yet grown 

 together. Upper side of 

 figure is posterior. 



sunken in deep bony pits, formed by the bones in the eye- 

 brows, nose and cheek which thus ensures them against injuries. 



The ears are best protected of all, 

 since the real hearing parts are 

 completely inclosed in hard bone 

 inside the skull, only narrow pass- 

 ages connecting them with the 

 exterior. 



THE APiPENDICULAR SKELETON 



The Shoulder and the Arm. Each 

 shoulder, or pectoral girdle, is made 

 of two bones. (1) The shoulder 

 blade is an oddly shaped, triangular 

 bone on the back of the shoulder 

 joint. To this scapula, the upper 

 bone of the arm is hinged (Fig. 

 127) and a shallow cavity 

 in it forms a part of the 

 shoulder joint. (2) The 

 collar bone or clavicle, 

 which is slender and in 

 such a position as to be 

 easily broken, extends 

 from the sternum to the 

 shoulder joint, thus brac- 

 ing the scapula; Fig. 

 120. 



The first bone in the 

 arm is called the humer- 

 us and extends from the 

 shoulder to the elbow, 

 Fig. 128. Between the 



elbow and wrist are two bones, the radius and ulna, the 

 former on the same side as the thumb. The ulna alone 



-Jcopula 



Humeruf 



FIG. 127. THE BONES THAT FORM THE 

 SHOULDER JOINT 



