58 ELEMENTARY TISSUES. 



and examined with, a high power of the microscope, it will 

 be found composed, according to Sharpey, of a finely 

 is* reticular structure, formed ap- 



parently of very slender fibres 

 decussating obliquely, but coales- 

 cing at the points of intersection, as 

 if here the fibres were fused rather 

 than woven together (fig. 18). 



In many places these reticular 

 lamellae are perforated by tapering 

 fibres, resembling in character the 

 ordinary white or rarely the elastic 

 fibrous tissue, which bolt the neigh- 

 bouring lamellae together, and may 

 be drawn out when the latter are torn asunder (fig. 19). 



Bone is developed after two different fashions. In one, 

 the tissue in which the earthy matter is laid down is a 

 membrane, composed mainly of fibres and granular cells, 

 like imperfectly developed connective-tissue. Of this kind 

 of ossification in membrane, the fiat bones of the skull 

 are examples. In the other, and much more common case, 

 of which a long bone may be cited as an instance, the 

 ossification takes place in cartilage. 



In most bones ossification begins at more than one 

 point; and, from these centres of ossification, as they are 

 called, the process of deposition of calcareous matter 

 advances in all directions. Bones grow by constant de- 

 velopment of the cartilage or membrane between these 

 centres of ossification, until by the process of calcification 

 advancing at a quicker rate than the development of the 

 softer structures, the bone becomes impregnated through- 



* Fig. 1 8. Thin layer peeled off from a softened bone, as it appears 

 under a magnifying power of 400. This figure, which is intended 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 (from 

 Sharpey). 



