FORMATION OF BONE. 41 



The ossification of spheri-formed bones, Fig. 6.* 

 begins by one nucleus, as in the wrist ; and 

 that of irregularly shaped bones by different 

 nuclei, as in the vertebrae. 



Some bones are completely formed at the 

 time of birth, as the small bones of the ear. 



The generality of bones are incomplete 

 until the age of puberty, or between the fifteenth and twentieth 

 year, and in some few instances until a later period. 



In children, many parts of bones, particularly the ends of 

 long bones, are distinct from the bodies ; they are called 

 epiphyses, and can be readily separated from the bodies of 

 bones, by boiling, or by maceration in water. 



The epiphyses begin to appear after the body of the bone is 

 ossified, and are themselves ossified at seven or eight years of ,' 

 age, though their external surface is still somewhat cartilagi- 

 nous. 



They are joined to the body of the bone by the cartilages, 

 which are thick in children, but gradually become thinner as 

 ossification advances, till at last, in the adult, the external 

 marks of division are not to be seen, though frequently some 

 mark of distinction may be observed in the cancelli. 

 The development of bones is the final result of several suc- 

 cessive changes. In the foetus the bone is at first represented, 

 by a soft gelatinous mass, continuous throughout as one piece, 

 and in which there is no appearance of joints. The consistence 

 of this matter gradually increases, and presents a cartilaginous 

 appearance, about the second or third months of foetal life. At 

 the same period a separation is manifested at the place of the 

 joints. A third change takes place in the cartilage, which is 

 that of ossification ; this commences in some of the bones, 

 between the second and third months of foetal life, at various 



* Parietal boss of the infant at birth magnified, showing the central point of 

 ossification. At first sight the vascular canals, resemble radiated lines, but with 

 a little attention, they will be found to be vascular channels, slightly tortuous, 

 and originating near the centre of the boss or protuberance from the foramina 

 in Ihe newly formed bone. p. 



4* 



