58 



THE CONNECTIVE TISSUES 



[CH V. 



are concentrically arranged around the Haversian canals to the 

 number of six to eighteen around each. 



3. Interstitial lamellae; these connect the systems of Haversian 

 lamellae, filling the spaces between them, and consequently attaining 

 their greatest development where the Haversian systems are few, and 

 vice versd. 



The ultimate structure of the lamellae is fibrous. If a thin film 

 be peeled off the surface of a bone, from which the earthy matter has 

 been removed by acid, and examined with a high power of the ^icro- 

 scope, it will be found composed of very slender fibres decussating 



FIG. 86. Thin layer Tpeeled 

 off from a softened bone. 

 This figure, which is in- 

 tended to represent the 

 reticular structure of a 

 lamella, gives a better 

 idea of the object when 

 held rather farther off 

 than usual from the, eye. 

 x 400. (Sharpey.) 





Fio. 87. Lamellae torn oft' from a decalcified human- 

 parietal bone at some depth from the surface. 



a, a, Lamellae, showing intercrossing fibres ; 



b, darker part, where several lamellae are^super- 

 posed ; c, perforating fibres. Apertures, through 

 which perforating fibres had passed, are seen 

 especially in the lower part, a, a, of the figure. 

 (Allen Thomson.) 



obliquely, but coalescing at the points of intersection, as if here the 

 fibres were fused rather than woven together (fig. 86). These are 

 called the intercrossing fibres of Sharpey ; they correspond to the white 

 fibres of connective tissue, and form the source of the gelatin obtained 

 by boiling bone. 



In many cases, as in the parietal bone, the lamellae are perforated 

 by tapering fibres called the perforating fibres of Sharpey, resembling 

 in character the ordinary white or more rarely the elastic fibres, 

 which bolt the neighbouring lamellae together, and may be drawn out 

 when the latter are torn asunder (fig. 87). These perforating fibres 

 originate from ingrowing processes of the periosteum, and in the adult 

 still retain their connection with it. 



