76 ANATOMY AND PHYSIOLOGY 



Sternum Presents a number of small centers, imbedded in cartil- 



lage. 



Upper extremity Shoulder-girdle ossified at acromial end of clavicula and 



in body of scapula; other parts are cartilage. 

 Long bones Shafts partially ossified. 

 Carpus : all bones entirely cartilaginous. 



Lower extremity . . . Long bones Shafts partially ossified; at the knee the 



ends of the femur and the tibia have begun to ossify. 



Tarsus three bones (talus, calcaneus, and cuboideum) 



have begun to ossify. 

 The metacarpal, metatarsal and phalangeal bones have 



thin lines of osseous tissue before birth. 

 At age of 20 years 

 Head 



Hands 



All completed. 



Feet 



Long bones All completed except tibia and fibula whose upper ends 



are not yet united with the shafts. 

 Ribs 



, Are in two pieces each. 



Sternum J 



Shoulder-girdle Clavicula, sternal end still separate. Scapula soft at 



borders and processes. 

 Pelvic-girdle Hip-bones (ossa coxae) completed. Sacrum and coccyx 



still in two or more pieces. 



Spinal column All parts ossified. 



At age of 25 years : . The skeleton is practically completed. The bones are 



strong, and the 'proper proportions of animal and 



mineral matter are preserved during adult life. 

 The coccyx may unite with the sacrum in middle life, 



thus modifying one of the diameters of the pelvic 



outlet. 

 In old age : There is no more growth. The supply of animal 



matter decreases, and the bones become brittle so 



that they may be easily broken. 



POINTS OF PRACTICAL INTEREST CONCERNING THE BONES IN 



INFANCY 



First, the baby's bones are soft, and are still largely composed 

 of cartilage. Second, since the process of ossification is going on 

 continually, the proper shape of the cartilage should be preserved 

 in order that the shape of the future bone may be normal. In 

 infancy the skull bones are movable as well as soft, and the shape of 

 the baby's head may be altered by pressure. Witness the Flathead 

 Indians, who bind a board across the top of the infant's skull. 



