OSTEOLOGY 





ferential, or by some authors primary or fundamental lamellae, to distinguish them 

 from those laid down around the axes of the Haversian canals, which are then 

 termed secondary or special lamellae. 



The Haversian canals, seen in a transverse section of bone as round holes at or 

 about the center of each Haversian system, may be demonstrated to be true canah 

 if a longitudinal section be made (Fig. 74). It will then be seen that the canah 

 run parallel with the longitudinal axis of the bone for a short distance and then 

 branch and communicate. They vary considerably in size, some being as much as 

 0.12 mm. in diameter; the average size is, however, about 0.05 mm. Near the 

 medullary cavity the canals are larger than those near the surface of the bone. 

 Each canal contains one or two bloodvessels, with a small quantity of delicate 

 connective tissue and some nerve filaments. In the larger ones there are also 

 lymphatic vessels, and cells with branching processes which communicate, through 

 the canalculi, with the branched processes of certain bone cells in the substance 

 of the bone. Those canals near the surface of the bone open upon it by minute 

 orifices, and those near the medullary cavity open in the same way into this space, 

 so that the whole of the bone is permeated by a system of bloodvessels running 

 through the bony canals in the centers of the Haversian systems. 



The lamellae are thin plates of bony tissue 

 encircling the central canal, and may be com- 

 pared, for the sake of illustration, to a number 

 of sheets of paper pasted one over another 

 around a central hollow cylinder. After 

 macerating a piece of bone in dilute mineral 

 acid, these lamellae may be stripped off in a 



FIG. 74. Section parallel to the surface 

 from the body of the femur. X 100. o, Haver- 

 sian canals; 6, lacunae seen from the side; c, 

 others seen from the surface in lamellae, which 

 are cut horizontally. 



Fid. 75. Perforating fibers, human parietal bone, decalcified. 

 (H. Mttller.) a, perforating fibers in situ; b, fibres drawn out of 

 their sockets; c, sockets. 



longitudinal direction as thin films. If one of these be examined with a high power 

 of the microscope, it will be found to be composed of a finely reticular structure, 

 made up of very slender transparent fibers, decussating obliquely; and coalescing 

 at the points of intersection; these fibers are composed of fine fibrils identical with 

 those of white connective tissue. The intercellular matrix between the fibers is 

 impregnated by calcareous deposit which the acid dissolves. In many places the 

 various lamellae may be seen to be held together by tapering fibers, which run 

 obliquely through them, pinning or bolting them together; they were first de- 

 scribed by Sharpey, and were named by him perforating fibers (Fig. 75). 



The Lacunae are situated between the lamellae, and consist of a number of oblong 



