1 8 Introduction to Animal Morphology . 



matrix is arranged in plates* around vascular canals {Haver- 

 sian canals), and is studded with corpusclesf which send 

 processes (canaliculi) in all directions.]: The lamellae are 

 pierced at right angles by rialcified rods.§ In development 

 sometimes the lime salts are laid down in the intercellular 

 substances, so that the connective tissue corpuscles become 

 bone-cells, but this simple form of bone development is rare. 

 Usually in the ossifying of cartilage the corpuscles first mul- 

 tiply and become arranged in columns. Protoplasmic masses 

 ascend in spaces or canals between these, and vessels from 

 the periosteum shoot into their intervals : then a granular 

 osseous matter is deposited along the vessels so that the 

 groups of corpuscles lie in spaces (primary areolae) bounded 

 by the spicular growth of the bone substance. At this stage 

 the corpuscles become granular and break up into smaller cell 

 masses, while by absorption the primary areolae are made to 

 communicate with each other, becoming secondary areolae 

 filled with a series of granular corpuscles (osteoblasts) and 

 free protoplasm. On the walls of these areolae are laid down 

 laminae of homogeneous bone matter (secondary bone forma- 

 tion), in which the floating granular cells are embedded, the 

 spaces occupied by them being called lacunae, and their pro- 

 cesses form the canaliculi. These secondary areolar spaces are 

 traversed by vessels and form Haversian canals, or, when 

 larger and irregular, form cancellous or spongy tissue. The 

 primary bone is granular, the secondarj' is at first homoge- 

 neous. 



Bone tissue thus formed may be compact, traversed by 

 vascular tubes {Haversian canals), or cancellous, with wide 



matter in the bones of a child, 33 per cent, in the adult, and 28 in very 

 senile bones. 



* The lamellae may be ist, around Jlaversian canals ; 2nd, intermediate 

 to such. Haversian systems; or 3rd, Peripheric : the latter are few {Tomes). 

 Each lamina consists, according to Sharpey, of densely decussated fibres. 

 The intermediate lamellae are parts of absorbed Haversian systems. 



t About 800 to a square millimetre in man. 



J Ending in fine points at the articular ends. 



§ The perforating fibres of Sharper, which when decalcified are tubular 

 {Toines and De Morgan). 



