66 NORMAL HISTOLOGY. 



Haversian systems of lamellae lie closely crowded 

 together, and again they lie at varying distances 

 from one another. In the latter case the interven- 

 ing space is filled up by other and irregular sets of 

 lamellae which do not correspond with the Haversian 

 lamellae, but pass off obliquely in various directions. 

 These are called, from their position relative to the 

 Haversian system, intermediate lame lice. Finally, at 

 the surface of the bone beneath the periosteum, and 

 sometimes at the inner surface adjacent to the me- 

 dullary cavity, are seen a series of lamellae which lie 

 parallel to the surfaces of the bone, and are called 

 general or circumferential lamellce. If we make a 

 longitudinal section of a long bone, we find that it 

 is traversed by a number of more or less longi- 

 tudinally arranged, branching, and communicating 

 canals, of varying size, in which lie the blood- and 

 lymph-vessels. It is around these canals, called 

 Haversian canals, that the Haversian lamellae are 

 grouped, and the variously shaped openings which 

 are seen in the transverse sections are transverse 

 sections of these vascular or Haversian canals. 

 Within the Haversian canals, when they are not en- 

 tirely filled with the blood-vessels, we find the latter 

 enclosed in a tissue identical with that filling the 

 medullary cavity, and presently to be described as 

 marrow. In the flat and irregular-shaped bones 

 essentially the same structural features are present, 

 but the lamellar arrangement is much less regular. 



