I30 ELEMENTARY BIOLOGY. [CHAl 



^. The periosteum ; a thin layer closely applied tc 

 the outer face of a.^ and staining with great inj 

 tensity. 



y. The ifiarrow ; composed of larger vacuolatec 

 (fat-laden) cells, and smaller rounded deeply- 

 stained ones {red marrow cells), 



S The nutrient vessels; in section as follows: — £ 

 larger ovoidal and thin-walled vein^ and a smalleij 

 cylindroidal and thick-walled artery^ lying close 

 together near the middle of the marrow. 



c. Search your sections for any which may have' 

 passed through a nutritive foramen ; if present, 

 note the relations of the periosteum to the 

 marrow. 



c. Examine your thinnest section under a high 

 power. fll 



a. The bony shaft ; seen to consist of a number of 

 concentric layers or lainellce, rendered distinc 

 under the action of the reagent. 



Find the middle lamella {b. a); it marks th 

 boundary line between an inner, more lightly 

 stained series [concentric or peri-medullary lamellce) 

 and an outer, more deeply stained series {circum- 

 ferential or subperiosteal lamellce). 



fi. The bone corpuscles ; minute fusiform or branch-' 

 ing cells, set along the lines of the above la- 

 mellae. Each clear and little stained, with a 

 deeply stained nucleus. (Cf connective tissue 

 corpuscle.) 



y. The periosteum ; if the section be a good one, 

 its innermost layer -will be seen to consist of a 

 row of small flattened cells {osteoblasts). 



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