34 ANATOMY AND PHYSIOLOGY FOR NURSES 



ing labor, especially in instrumental cases, from the 

 pressure of the child's head in its passage through the 

 outlet of the pelvis. 



The ossa innominata, or nameless bones, form the sides 

 and anterior wall of the pelvic cavity. They are divided 

 into three parts the ilium, the ischium, and the pubes; 

 in adults these become consolidated and form one bone. 

 At the junction of the three parts is found the acetabulum, 

 which articulates with the head of the femur. The up- 

 per border of the bone is called the crest of the ilium; the 

 low r er, the ischium; and the anterior, the pubes. The 

 anterior extremity of the iliac crest is called the anterior 

 superior spine of the ilium; that portion of the ischium 

 upon which we sit is the tuber osity; the junction of the 

 pubic bones is known as the symphysis. These are im- 

 portant landmarks. 



THE BONES OF THE UPPER EXTREMITY 



The bones of the upper extremity are the clavicle and 

 scapula (comprising the shoulder girdle), the humerus, 

 the radius and ulna, the carpal bones, the metacarpal 

 bones, and the phalanges. 



The clavicle or collar-bone, is shaped like the letter f, 

 and articulates with the sternum and the scapula. 



It has a wide range of motion, and this, together with its 

 exposed position and the fact that it is the only bony con- 

 nection between the trunk and the upper extremity, ex- 

 plains why the clavicle is more frequently broken than any 

 other single bone in the body. 



The scapula or shoulder-blade, is situated on the 

 posterior and lateral part of the thorax, overlying the 

 region included between the second and the seventh ribs. 

 The dorsal surface of the bone is traversed by an elevated 

 ridge the spine the outer extremity of which overhangs 

 the shoulder, and is known as the acromion. Just beneath 



