1100 



GENERAL ANATOMY OR HISTOLOGY. 



lined at all) by a delicate membrane. But this view was subsequently proved 

 to be erroneous, for examination of the structure of bone, when recent, led 

 Virchow to believe that the lacunae are occupied during life by a branched cell, 

 termed a bone-cell or bone-corpuscle, the processes from which pass down the 

 canaliculi a view which is noAv universally received (Fig. 627). It is by means of 

 these cells that the fluids necessary for nutrition are brought into contact with 

 the ultimate tissue of bone. 



The canaliculi are exceedingly minute channels, which pass across the lamellae 

 and connect the lacunae with the neighboring lacunae and also with the Haversian 

 canal. From this central canal a number of the canaliculi are given off, which 

 radiate from it, and open into the first set of 

 lacunae, arranged around the Haversian canal, 

 between the first and second lamellae. From 

 these lacunae a second set of canaliculi are 

 given off, which pass outward to the next 

 series of lacunae, and so on until they reach the 

 periphery of the Haversian system : here the 

 canaliculi given off from the last series of 

 lacunae do not communicate with the lacunae 

 of neighboring Haversian systems, but after 

 passing outward for a short distance form loops 



?&& m 





B ' 



m/ t^m 



%'m 



FIG. 627. Nucleated bone-cells and their processes, con- 

 tained in the bone-lacunse and their canaliculi respectively. 

 From a section through the vertebra of an adult mouse. 

 (Klein and Noble Smith.) 



FIG. 628. Section parallel to the surface 

 from the shaft of the femur. Magnified 100 

 times. a. Haversian canals, b, Lacuna' seen 

 from the side, c, Others seen from the sur- 

 face in lamellae which are cut horizontally. 



and return to their own lacuna. Thus every part of the Haversian system is 

 supplied with nutrient fluids derived from the vessels in the Haversian canals and 

 traversing the canaliculi and lacunae. 



The bone-cells are contained in the lacunae, which, however, they do not com- 

 pletely fill. They are flattened nucleated cells, which Virchow has shown are 

 homologous with those of connective tissue. The cells are branched, and the 

 branches, especially in young bones, pass into the canaliculi from the lacunae. 



If a longitudinal section is examined, as in Fig. 628, the structure is seen to be 

 the same. The appearance of concentric rings is replaced by that of lamellae or 

 rows of lacunae, parallel to the course of the Haversian canals, and these canals 

 appear like half-tubes instead of circular spaces. The tubes are seen to branch 

 and communicate, so that each separate Haversian canal runs only a short distance. 

 In other respects the structure has much the same appearance as in transverse 

 sections. 



In sections of thin plates of bone (as in the walls of the cells which form the 

 cancellous tissue) the Haversian canals are absent, and the canaliculi open into the 

 spaces of the cancellous tissue (medullary spaces), which thus have the same func- 

 tion as the Haversian canals in the more compact bone. 



