70 SKELETON. 



In the long bones a small ring is observed to form early near 

 their centre, and to be perforated on one side by the nutritious 

 artery. This ring has its parietes thin, but broad, and its cavi- 

 ty is the beginning of the medullary canal. It is formed of 

 very delicate fibres which advance towards the extremities of 

 the bone,* and at the same time increase in thickness; so that 

 at birth, the body or diaphysis is generally finished. Common- 

 ly, at a period subsequent to birth, but differing in the several 

 bones, their cartilaginous epiphyses also begin to ossify, by the 

 development in their centre of points of ossification, which pre- 

 sent the phenomena mentioned in the last paragraph but one. 

 The cartilaginous state of the epiphysis gradually disappears 

 by retiring from the articular end of the bone towards its dia- 

 physis; and, just before its complete removal, it appears as a 

 thin lamina, gluing the end or epiphysis of the bone to its body. 

 Several of the apophyses of the long bones are also formed from 

 distinct points of ossification. 



The ossification of the flat or broad bones begins by one or 

 more points, according to the bone being of a simple shape as 

 the parietal; of a double shape or symmetrical, as the frontal, 

 where there are two points of ossification ; or of a compound 

 shape, as the occipital and temporal, where there are several 

 points. The commencement of ossification in them, is also 

 manifested by the appearance of a red vascular spot in the 

 cartilaginous rudiment, in which the osseous matter is depo- 

 sited, and from which it progresses in radiated lines. The 

 periphery of this circle of rays presents intervals between the 

 fibres, giving it the appearance of the teeth of a fine comb: 

 these intervals are subsequently filled up by the sections of radii 

 starting from them, and so on successively till the bone is 

 finished. In the infantile head the several radii grow with a 

 pace nearly equal ; so that where the bones are angular, the 

 angles being most distant from the centre of ossification are 

 finished last of all, from which result the fontanels. Where the 

 bones are intended to be kept distinct from each other, their 

 fusion is prevented by a membranous partition; but when they 

 are to coalesce into one piece, only cartilage is found, which is 

 subsequently ossified. 



* Bichat, loc. cit. 



