OSSIFICATION 15 



The deposit of mineral matter begins in small spots, forming 

 centers of ossification which gradually increase in size until the 

 entire bone is completed. Long bones have always three centers 

 at first one for the shaft, and one for each extremity others 

 appearing later, at different dates. (The extremities are named 

 epiphyses, the shaft being the diaphysis) (see Fig. 9). The 

 principal parts of a bone are ossified separately, uniting with 

 each other after all are developed. Ossification begins before 

 birth in all bones except the coccyx, those of the carpus, and four 

 in the tarsus; but many bones remain in two or more pieces 

 during childhood and youth. 



The periosteum of bone has an inner layer in which, also, the 

 process of ossification goes on. Consequently, when it becomes 

 necessary to remove a portion of bone, if it can be done without 

 taking the periosteum away the bone will re-form. This has 

 occurred many times, particularly in the case of the mandible. 



The nutrition of bone. Bones have a free blood supply from 

 a network of small arteries in the periosteum. One special artery, 

 larger than the others, enters the nutrient canal which leads to 

 the interior of the shaft (this vessel is called the nutrient artery). 



The skeleton of the body comprises 200 bones, as follows: 



In the cranium 8 



In the face , 14 



In the spinal column 24 



In the pelvis 4 



In the upper extremities 64 



In the lower extremities 60 



Ribs 24 



Os hyoides i 



Sternum. . , i 



200 



These are joined together or articulated to form the hard, 

 strong framework of the body the natural skeleton. 



In addition to these, there are four bones in each ear called ossicles, or 

 "little bones," malleus, incus, stapes and so-called orbicular bone. 



