IJ2 



OSSEOUS SYSTEM. 



[sect. 91. 



neighbouring cells. I call these cells, in honour of their dis- 

 coverer, Virchows hone-cells, and will, further on, discuss their 

 great physiological importance. 



Although Virchoiv's cells are, properly, of more importance, yet, 

 in the following description, we shall refer more to the bone- 

 cavities accurately surrounding them, because in the bones which 



Fig. 71 



■"*m 



ftp**!.. 



'ap* 



are usually the subject of 

 examination the inclosing 

 cavities are almost alone 

 visible. These are oval, 

 flattened spaces of o - oi'" 

 in medium length, 0004'" 

 broad, and 0'003'" thick, 

 which, both from their 

 borders and surfaces, but 

 especially from the latter, 

 give off a large number 

 of very fine canals, of 

 0-0005'" to 00008'" in 

 diameter — the canaliculi. 

 The lacunas are equally 

 numerous in both kinds 

 of the above-described 



From a transverse section of the diaphysis of the hu- 

 merus, magnified 350 times, a. Haversian canals ; b. lacunae 

 with their canaliculi in the lamellae of the same ; c. lacunae c,t7c+»me nf limpllrp and 

 of the interstitial lamellae; d. others at the surface of the _»Yalt;illo Ul lciuiciicc, cuiu. 

 Haversian systems, with canaliculi going off from one side, ^g situated SO closelv to 



each other, that, according to Harting, there are from 709 to 11 20, 

 or, on an average, 910 in a square millimeter. They generally lie 

 in the lamellas, but also between them, and are arranged, without 

 exception, with their broad sides parallel to the direction of the 

 lamellas. The canaliculi which proceed from them take an irre- 

 gular and often a bending course, branch out in various ways, and 

 penetrate the osseous substance in all directions. For the most 

 part, however, they pass from the two surfaces of the lacunas 

 straight through and across the lamellae, and also from the two 

 poles of the lacunas in a direction parallel to the Haversian canals. 

 It is only in certain places that the canaliculi terminate in blind 

 extremities ; in all other localities a certain number of them ana- 

 stomose in various ways with the canaliculi of neighbouring lacunas, 

 whilst another part open into the vascular canals, the medullary 

 cavities and spaces of the spongy substance, or terminate free upon 

 the surface of the bone. There is thus formed a connected system 

 of cavities and canals traversing the whole osseous substance, by 



