52 



CONSCIOUS NERVOUS OPERATIONS 



spongy bone around the cavity which contains the mar- 

 row (lower end of Fig. 37). 



In the enlarged articular extremities of the bone, how- 

 ever, the reverse is the case. The firm, compact part 



forms only a thin 

 layer on the sur- 

 face, the rest being 

 a loose, spongy net- 

 work of bony mat- 

 ter, with the spaces 

 filled with a soft, 

 red substance called 

 red marrow. 



Interlacing chan- 

 nels, called the Ha- 

 versian canals, run 

 through the whole 

 substance of a bone, 

 in the densest as 

 in the more porous 

 parts. The perios- 

 teum is richly sup- 

 plied with blood ves- 

 sels, and from them 

 minute branches en- 

 ter the bone itself 

 and run along the 

 Haversian canals. 

 Other blood vessels reach the solid portion of the bone 

 from within, through the medullary canal of the center of 

 the bone, and thus nutriment is conveyed to every part. 



Each Haversian canal is surrounded by a set of hard 

 bony plates, and between the plates, or lamellce, are little 



Fig 87. 



Longitudinal section of the upper 

 end of the tibia. 



