BONE. 



575 



stance, or shaft, we shall find it to be slightly porous, 

 or rather occupied, both on its external and internal sur- 

 faces, by a series of very minute canals, which, from their 

 having been first described by our countryman Clopton 

 Havers, are termed to this day the Haversian canals, and 

 serve for the transmission of blood-vessels into the interior 

 of the bone. Further than this we cannot proceed without 

 optical assistance; but if now a thin transverse section 

 of the same bone be made, and be examined by the micro- 

 scope with a power of 200 linear, we shall see the Haversian 

 canals very plainly, and around 

 them a series of concentric bony 

 lamince, from three to ten or 

 twelve in number. If the sec- 

 tion should consist of the entire 

 circle of the shaft, we shall 

 notice, besides the concentric 

 laminae round the Haversian 

 canals, two other series of la- 

 minoe, the one around the 

 outer margin of the section, 

 the other round the inner or 

 medullary cavity. Between 

 the laminae is situated a con- 

 centric arrangement of spider- 

 like looking bodies, which have, Fig ^\S.A 

 by different authors, received 

 the name of osseous corpuscles, 

 lacunae, or bone-cells, according 

 as to whether they were ascer- 

 tained to be solid or hollow : 

 these bone-cells have little tubes or canals radiating from 

 them, which are termed canaliculi by some authors, and 

 tubes and pores by others: those bone-cells which are 

 nearest the Haversian canals have the canaliculi of that 

 side radiating towards the opening into the Haversian 

 canals ; whilst the canaliculi of the opposite side com- 

 municate with those of the layer of canaliculi more ex- 

 ternal to them; and those in the outer row have most 

 of their canaliculi given off from that side of the bone- 

 cell which is nearest its own Haversian canal: hence 



transverse section of the 

 Femur, or ley-bon" of an Ostrich, 

 (magnified 95 diameters.) When 

 contrasted with the preceding 

 figure, it will be noticed that the 

 Haversian canals are much smaller 

 and more numerous, and many of 

 them run in a transverse direction. 



