BONE. 75 



of a sponge. The diaphyses of long bones as well as the outer 

 parts of small and flat bones consist of compact bone substance, 

 while the epiphyses of long bones and the middle of short and 

 flat bones are made up of spongy bone. 



If we examine a longitudinal section of a bone which has 

 been for some time macerated, we observe with low magnifica- 

 tion broad canals which run more or less parallel to the longi- 

 tudinal axis (Fig. 39). These are connected by transverse 

 canals, and form altogether a complete canal system. These 

 so-called Haversian canals are in macerated bone empty, because 

 the blood-vessels which they contain in life have been dissolved 

 by the macerating fluids. 



Everywhere in the ground substance there are spaces, the 

 so-called bone lacunce, in which before maceration the bone cells 

 are contained. These are arranged in rows which are more 

 or less parallel with the Haversian canals. 



On examination of a cross-section of bone (Fig. 40), we 

 notice that the Haversian canals are round and the transverse 

 canals are cut longitudinally. Around the Haversian canals 

 the bone lacunae are arranged in concentric rows. With 

 higher magnification the ground substance is seen to be 

 made up of lamellae lying in groups at various angles to one 

 another. In compact bone we may distinguish several kinds 

 of lamella : 



1. Special lamellae of the Haversian systems, or Haversian 

 lamellce, are those arranged concentrically around the Haversian 

 canals. All those lying about one Haversian canal make up 

 what is known as an Haversian system of lamellce. The num- 

 ber of lamellae in a system may vary from three to twenty or 

 more, although it is usually from eight to fifteen. 



2. Interstitial or intermediary lamellae, are those which fill up 

 the spaces between adjacent Haversian systems. These are 

 divided into real interstitial lamellae, which are formed from 

 the periosteum and run in the same direction as the outer 

 ground lamellae ; and false interstitial lamellae, which are merely 

 remains of Haversian systems that have been destroyed (see 

 Skeletal System). 



