BONE. 



379 



actions, a most excellent account of the " Intimate Structure of Bone. 1 ' 

 From this paper we propose to show the valuable results to be ob- 

 tained by a microscopic investigation of bone. 



" Bone consists of a hard and soft part ; the hard is composed of 

 carbonate, phosphate, and fluate of lime, and of carbonate and phos- 

 phate of magnesia, deposited in a cartilaginous or other matrix ; whilst 

 the soft consists of that matrix, and of the periosteum which invests 

 the outer surface of the bone, and of the medullary membrane which 

 lines its interior or medullary cavity, and is continued into the mi- 

 nutest pores. If we take for examination a long bone of one of the 

 extremities of the 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 throughout the whole of it, or else is 

 entirely or partially filled up with a cellular bony strupture, which 

 cells are termed cancelli, and the structure a cancellated structure. On 



fig. 180. 



1. A transverse section of the humerus, or fore-arm bone, of a Turtle (Chelonia mydas). 



It exhibits traces of Haversian canals, with a slight tendency to a concentric ar- 

 rangement of bone-cells around them. The bone- cells are large and very numerous, 

 but occur for the most part in parallel rows. 



2. A transverse section of the femui", or leg-bone, 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 trans- 

 verse direction. 



a more careful examination of the bony substance, or shaft, we shall 

 find it to be slightly porous, or rather occupied, both on its external 

 and internal surfaces, by a series of very minute canals, which, from 



