48 



understood, and a minute fragment would have sufficed for this pur- 

 pose. Before coming, however, to the immediate object of this paper, 

 it will be necessary that I point out to you briefly the different parts 

 of which a bone may be said to consist; and, as there are many 

 members of our small community who do not practise the healing art, 

 and have not, therefore, made the intimate structure of the animal 

 body their particular study, I trust that, by a slight description, I 

 shall be enabled to render the subject of which I am about to treat 

 perfectly intelligible to all. 



Every bone may be said to consist of two parts, a hard and a soft 

 part : the hard is composed of carbonate and phosphate of lime, and 

 of carbonate and phosphate of magnesia, deposited in a cartilaginous or 

 other matrix ; whilst the soft consists of that matrix, and of the peri- 

 osteum which invests the outer surface of the bone, and of the medullary 

 membrane which lines its interior or medullary cavity, and is conti- 

 nued into the minutest pores. If we take for examination a long bone 

 of one of the extremities, say a femur, of a human subject, or of any 

 mammalian animal, we shall find that it consists of a body or shaft 

 and two extremities : if a vertical section of such a bone be made, we 

 shall also find that the middle of the shaft contains a central cavity, 

 termed the medullary cavity, which extends as a canal thronghout the 

 whole of it, or else is entirely or partially filled up with a cellular 

 bony structure, which cells are termed cancelli, and the structure a 

 cancellated structure. On a more careful examination of the bony 

 substance or shaft, we shall find it to be slightly porous, or rather oc- 

 cupied, both on its external and internal surfaces, 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 in our investiga- 

 tion without optical assistance ; but if now a thin transverse section 

 of the same bone be made, and be examined by the microscope with 

 a power of 200 linear, we shall see the Haversian canals very plainly, 

 and around them a series of concentric bony laminae, from three to ten 

 or twelve in number. If the section should consist of the entire 

 circle of the shaft, we shall notice, besides the concentric laminae 

 around the Haversian canals, two other series of laminae, the one 

 around the outer margin of the section, the other around the inner or 

 medullary cavity. Between the laminae is situated a concentric ar- 

 rangement of spider-like looking bodies, which have, by different 

 authors, received the names of osseous corpuscles, calcigerous cells, 



