Chap. IV] 



CONNECTIVE TISSUES 



43 



"^'mm 



amount of inorganic matter in the bones of the aged renders the 

 bones more brittle, so that they break easily and heal with diflSculty. 



Rachitis or Rickets. — In the disease called rickets, quite com- 

 mon among poorly nourished children, there is not sufficient min- 

 eral matter, so that the bones are flexible, bend 

 easily, and may be permanently misshapen. 



Structure of Bone. — On sawing a bone it 

 will be seen that in some parts it is open and 

 spongy, whilst in others it is dense and close 

 in texture, appearing like ivory. We thus dis- 

 tinguish two forms of bony tis sue : — 



(1) The cancellated, or spongy. 



(2) The dense, or compact. 

 On closer examination, however, it will be 



seen that the bony matter is everywhere po- 

 rous, and that the difference between the two 

 varieties of tissue arises from the fact that the 

 compact tissue has fewer spaces and more 

 solid matter between them, while the can- 

 cellated has larger cavities and more slender 

 intervening bony partitions. In all bones 

 the compact tissue is the stronger ; it lies on 

 the surface of the bone and forms an outer 

 shell or crust, whilst the lighter, spongy tissue 

 is contained within. The shafts of the long 

 bones are almost entirely made up of the com- 

 pact substance, except that they are hollowed » u 

 out to form a central canal, — the medullarv j I 

 canal, — which has a fibrous lining called en- z e 

 dosteum, and contains marrow. ^ 



The hard substance of both varieties is ar- 

 ranged in bundles of bony fibres, or lamellae 

 (layers) . Fig. 19. — Vertical 



T 11 1 u 1 Section of a Long 



Cancellated bone. — In cancellated bone the bone. (Gerrish.) 

 lamellae join and meet together so as to form 

 a structure resembling lattice- work {cancelli), whence this tissue 

 receives its name. In the interstices of this kind of bone we find 

 the blood-vessels supported by the marrow. 



Compact bone. — In compact bone the lamellae are usually arranged 



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