

Chap, vii.] BONE. 53 



V 

 in open and free communication with lymphatic 



vessels of the marrow spaces and Haversian canals. 



65. In the bone matrix, each lacuna contains also 

 a nucleated protoplasmic cell, called the bone cell, which, 

 however, does not fill it completely. In the young 

 state, the cell is branched, the branches passing into 

 the canaliculi of the lacunae ; but in the old state very 

 few processes can be detected on a bone cell, which, 

 with its lacuna and canaliculi, is called a bone cor- 

 puscle. 



66. According to the arrangement of the bone 

 substance, we distinguish compact from spongy sub- 

 stance. The former occurs in the shaft of tubular 

 bones and in the outer layer of flat and short bones. 

 Its lamellse are arranged as : (a) concentric or Haversian 

 lamellce, directly surrounding the Haversian canals 

 (Fig. 33A). These are fine canals of varying lengths 

 pervading the compact substance in a longitudinal direc- 

 tion, and anastomosing with one another by transverse 

 or oblique branches. The Haversian canals near the 

 marrow cavity are larger than those near the perios- 

 teum. As a matter of fact, those next to the marrow 

 cavity become gradually enlarged by absorption, until 

 finally they are fused with the marrow cavity. Each 

 Haversian canal contains a blood-vessel, one or two 

 lymphatics, and a variable amount of marrow tissue. 

 These canals open both into the marrow cavity and on 

 the outer surface into the osteogenetic layer of the peri- 

 osteum, and they form the means by which the latter 

 remains in continuity with the marrow. They are 

 surrounded by numbers of concentric bone lamellae, 

 with the bone corpuscles between them, and this is a 

 system of concentric lamellce. Near the external sur- 

 face of the compact substance the number of lamella 

 in each system is smaller than in the deeper parts. 

 (6) Between these systems of concentric lamella are 

 the interstitial or ground lamellce; they run in various 



