DEVELOPiMENT OF BONE. 4ll 



The growth of bone in length takes place at the extremity of the dia- 

 physis, and in bulk by fresh deposition on the surface ; while the medul- 

 lary canal is formed and increased by absorption from within. 



The period of ossification is different in different bones ; the order of 

 succession may be thus arranged : 



During the fifth week, ossification commences in the clavicle, lower 

 jaw, and upper jaw. 



During the sixth week, in the femur, humerus, tibia, radius, and ulna. 



During the seventh and eighth weeks, in the fibula, frontal, occipital, 

 sphenoid, ribs, parietal, temporal, nasal, vomer, palate, vertebrae, first 

 three pieces of sacrum, malar, metacarpus, metatarsus, third phalanges of 

 the hands and feet, and ilium. 



During the third month, in the first and second phalanges of the hands 

 and feet, lachrymal bone, and ischium. 



During the fifth month, in the mastoid portion of the temporal, ethmoid, 

 inferior turbinated, sternum, os pubis, and last two pieces of sacrum. 



During the sixth month, in the body and odontoid process of the axis, 

 and in the calcaneus. 



During the seventh month, in the astragalus. 



During the tenth month, in the cuboid bone and os hyoides. 



During the first year, in the coracoid process of the scapula ; first piece 

 of the coccyx, inferior turbinated bone, last piece of the sternum, anterior 

 arch of the atlas, os magnum, os unciforme, and external cuneiform bone. 



During the third year, in the cuneiform of the carpus, internal cuneiform 

 of the tarsus, and patella. 



During the fourth year, in the middle cuneiform and scaphoid of the 

 tarsus. 



During the fifth year, in the trapezium and os semilunare. 



During the seventh year, in the second piece of the coccyx. 



During the eighth year, in the scaphoid of the carpus. 



During the ninth year, in the os trapezoides. 



During the twelfth year, in the os fisiforme and third piece of the coccyx. 



During the eighteenth year, in the fourth piece of the coccyx. 



The ossicula auditus are the only bones completely ossified at birth ; the 

 vertebra are not completed until the five-and-twentieth year. 



The entire osseous framework of the body constitutes the skeleton, which 

 in the adult man is composed of two hundred and forty-six distinct bones. 

 They may be thus arranged : 



Head 8 



Ossicula auditus 6 



Face 14 



Teeth . 32 



Vertebral column, including sacrum and coccyx 26 



Os hyoides, sternum, and ribs 26 



Upper extremities 64 



Lower extremities 62 



Sesamoid bones 8 



246 



The skeleton is divisible into : 1. The vertebral column, or central 

 2, The head and face, or superior development of the central axis. 

 5 D 



