76 ELEMENTAET PHTSIOLOGT. [VII. 



origin of two cells from one by oblique 

 division. 



c. A layer of cells much larger than the previous 

 ones, •with clear cell-substance (ia the speci- 

 men probably shrunken) and a distinct 

 nucleus ; they are also arranged in rows and 

 have only a small amount of matrix between 

 them. 



d. The large irregular cavities below this layer 

 surrounded by bone matrix, and containing 

 many osteoblasts, cells very similar in ap- 

 pearance to white blood corpuscles, but 

 larger, most of them are in contact with 

 the bone matrix. In the centre of some of 

 the cavities may also be seen a blood-vessel 

 with surrounding connective tissue. 



e. Osteoclasts may be seen here and there in 

 contact with the bone matrix ; they are large 

 multinuclear cells, and where they touch the 

 bone are often striated at right angles to the 

 surface. 



2. Imbed a piece of the shaft of any long bone* of a 

 foetal mammal that has been preserved in picric 

 or chromic acid, any remaining salts in the bone 

 may be extracted by placing it for a day in spirit 

 containing '5 p.c. nitric acid. Cut transverse 



1 Instead of these, seotions may be made of the lower jaw of a 

 foetal mammal; the developing snb-maxillaiy bone shews admirably 

 the osteoblasts and osteoclasts but the section is confasing to 

 beginners owing to the number of other tissues present. 



