54 ELEMENTS OF HISTOLOGY. [Chap.vn. 



directions, and in reality fill the interstices between 

 the systems of the Haversian or concentric lamellse. 

 Near the external surface of long bones they have pre- 

 eminently a direction parallel to the surface. These are 

 the circumferential lamellce of Tomes and de Morgan. 



i^lT&^> UteK-^ s.v?&U 





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



a, Concentric lamellae arranged around the Haversian canals, cut across; 

 b, interstitial or ground lamellas. The bone lacunas are seen between the 

 bone lamellae. (Atlas.) 



The lamellae 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 fine, 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; 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 are of 

 the shape of spicules and septa, called bone trabeculce, 



