37 



LESSON X. 



CANCELLATED BONE, DEVELOPING BONE, 

 AND BONE MARROW. 



(a) Cancellated Bone. 



The head of a long bone taken from a young animal was 

 divided into small pieces, hardened in mercuric chloride, decal- 

 cified in a 1% solution of hydrochloric acid, stained in Delafield's 

 hsematoxylin, embedded in paraffin, and sectioned. Sections were 

 fixed to cover glasses, and counter-stained in eosin, dehydrated, and 

 cleared in oil of bergamot. Mount in balsam. 



Study first under low power. Observe the network of 

 trabeculse. The spaces bounded by them are filled with 

 marrow cells. Under high power a layer of osteoblasts is 

 often seen lining the spaces. Fragments of calcified car- 

 tilage, taking the stain more deeply, may be seen in the 

 trabeculae. Sketch as seen under high power. 



(b) Developing Bone- / 



One of the developing bones removed from a foetal limb was 

 hardened and decalcified in picro-sulphuric acid, embedded in cel- 

 loidin, sectioned, and stained in hsematoxylin and eosin. Sections 

 are now in oil of bergamot, and are to be mounted in balsam. 



Study first under low power. If the section comes 

 from the center of the bone it will show the following areas, 

 named in order as they present themselves when the sec- 

 tion is moved from the articular surface toward the middle 

 of the shaft, where ossification is most advanced : 



( 1 ) Area of articular cartilage. 



(2) Area of flattened cartilage cells, arranged in rows. 



(3) Area of enlarged cartilage cells. Calcification 

 may have taken place in the matrix between the rows. 



(4) Area of ossification. Osseous substance is being 

 deposited by the osteoblasts on the calcified trabecuiae of 

 the cartilage. Small arterioles and capillaries surrounded 



