54 ELEMENTS OF HISTOLOGY. [Chap. VH. 



directions, and in reality fill the interstices between 

 the systems of the Haversian or concentric lamellae. 

 Near the external surface of long bones they have pre- 

 eminently a direction parallel to the surface. These are 

 the circumferential lamellw of Tomes and de Morgan. 



a 



Fig. 33A. Compact Bone Substance in Cross Section. 



a. Concentric lamcllaa arranged around the Haversian canals, cut across; 

 b, intermediate or ground lamellie. The bone lacunae are seen between the 

 bone lamellae. (Atlas.) 



The lamella of compact bone are perforated by per- 

 pendicular petrified fibres, the perforating fibres of 

 Sharpey. They form a continuity with the fibres of 

 the periosteum, from which they are developed. 



Some of these fibres are smaller than the rest, and 

 of the nature of elastic fibres. 



67. Spongy bone substance occurs in the end of the 

 shaft, in the apophyses, in short bones, and .in the 

 diploe of flat bones. The cavities or meshes of the 

 spongy substance are called Haversian spaces or can- 

 celli; they intercommunicate with one another, and are 

 filled with marrow, which in the young and growing 

 state is generally of the red variety. The firm parts 

 form spicules and septa, called bone trabeculce, 



