94 



HISTOLOGY 



teristic figure. Such vessels are said to occupy Haversian canals (named 

 for the English anatomist, Clop ton Havers). Volkmann's canals contain 

 vessels, but they are not surrounded by concentric lamellae. An Haver- 

 sian canal often contains two vessels, an artery and a vein, together 

 with a small amount of connective tissue and occasional fat cells; flattened 

 osteoblasts may rest against the surrounding bone, and send processes 

 into it. The concentric lamellae enclosing an Haversian canal constitute 



Resorption line. 



Volkmann's canals. 



Periosteum. 



-7-"* Periosteal lamellae. 

 " " _ 1 "jj --" Perforating fibers. 



- Y \--.7 -!./.-"/;'- 



I ', '. '.," - v:--^-"- Haversian lamellae. 



.;" . x -,', -.' ^^.---1 Haversian cana!. 



'" ' /.'>;."" -V''^V" : ^-' ; ,' : '- .-.-" Q y~^ 



*-''''./'- /: . 0, -'-"- -- 



' : '?''' :: ^i-'^-^ ; -'^ : - ft-~ interstiti 



' '-"^Jft-'V-^ .--'"'' ly ?'"; .'-''.'.' ."' < ^^'~' ~-~JU~ ^ '."' i'V-'' ,''/*V' 



ial lamellae. 



. Endosteal lamellae. 



. Marrow. 



FIG. 80. PART OF A CROSS SECTION OF A DECALCIFIED PHALANX FROM AN ADULT. 



an Haversian system. Interstitial lamella, irregularly arranged, fill the 

 intervals between the Haversian systems. 



The way in which the compact bone of the adult is formed from the 

 trabecular network of the embryo is indicated in the diagram, Fig. 81 

 (cf. also Fig. 73). After an area of vascular tissue has been surrounded 

 by bone, the osteoblasts form lamella?, gradually closing in from all 

 sides until only a slender canal remains. Successive stages are shown 

 in Fig. 81, B. V., H. C 1 , and H. C 2 , respectively. The deposition of the 

 concentric lamellae is not continuous. It is interrupted by periods of 



