130 ELEMENTARY BIOLOGY. [CHAP. 



/?. The periosteum ; a thin layer closely applied to 

 the outer face of a., and staining with great in- 

 tensity. 



y. The marrow ; composed of larger vacuolated 

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

 stained ones (red marrow cells]. 



8 The nutrient vessels; in section as follows: a 

 larger ovoidal and thin-walled vein, and a smaller 

 cylindroidal and thick-walled artery, lying close 

 together near the middle of the marrow. 



e. 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. 



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

 concentric layers or lamella, rendered distinct 

 under the action of the reagent. 



Find the middle lamella (b. a); it marks the 

 boundary line between an inner, more lightly 

 stained series (concentric or peri-medullary lamella) 

 and an outer, more deeply stained series (circum- 

 ferential or sub-periosteal lamella}. 



ft. 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). 



