HISTOLOGY. 47 



blood vessels into the bones. The lamellae, arranged 

 around the Haversian canal, are called the Haversian 

 lamellae. The lamellae running parallel with the outer 

 surface of the bone are called the ground lamellae, and 

 those running between the Haversian system, are called 

 the interstitial lamellae. There are little canals run- 

 ning from the periosteum to the nearest Haversian la- 

 mellae. These canals are called Volkmann's canals. 

 Occasionally uncalcified lines are seen passing ob- 

 liquely or transversely through the lamellae. These, 

 are called the lines of Sharpey. The periosteum 

 consists of fibrous connective tissue, and is divided 

 into two layers. One layer is the bone-forming 

 layer and the other is the bone-protecting layer. Bone- 

 marrow is composed of two kinds of cells, the red and 

 yellow. The yellow is mostly of the fat variety, and 

 the red is mostly of red blood cells. The blood vessels 

 of the bone tissue are distributed through the Haver- 

 sian system and the canals of Volkmann. The perios- 

 teum is richly supplied with blood vessels. 



Bone develops in two ways : centers of ossification 

 and perichondrial. The perichondrial is as follows: 

 the cells of the immature bone pass down the lines of 

 Volkmann and locate themselves in a center called a 

 center of ossification. Ossification means the depo- 



