80 NORMAL HISTOLOGY AND ORGANOGRAPHY, 



In the circumferential lamellae canals, called Volk- 

 manris canals, convey blood-vessels to the Haver- 

 sian canals. In the angular interstices, between the 

 Haversian systems, lamellae and canaliculi are found 

 arranged like those of the circumferential lamellae. 

 The shafts of long bones contain a marrow cavity. 

 At the ends the marrow cavity disappears, and the 

 bony structure becomes spongy with many inter- 

 stices and is then called cancellate bone. The middle 

 of flat bones is made up of a like loose structure 

 called diploe. 



Haversian canal. .. 



Fig. 49. Portion of a transversely ground disc from the shaft of a 

 human femur (Bohm and Davidoff). 



Periosteum. The periosteum is a dense, fibrous, 

 connective-tissue membrane that covers the bone 

 and is derived from the perichondrium of the carti- 

 lage. It is composed of two layers, (a) an inner 

 layer that contains many elastic fibers and osteo- 

 blasts, or bone-forming cells, known as the osteo- 

 genetic layer, and (b) an outer layer of coarse, 

 white, fibrous bundles where numerous blood-vessels 

 ramify and send branches to the Haversian canals. 



