ANALYSIS OF BONES. 



381 



which traverse the substance of the ttpe, and 

 communicate irregularly with each other. All 

 the different lacunae communicate by means of 

 the canaliculi with the Haversian canals ; so 

 that fluid may pass to every part of the osseous 

 substance, and thus convey fluid for nutrition. 

 They open, likewise, into the great medullary 

 canal, and into the cavities of the cancellated 

 texture. Blood corpuscles cannot pass along 

 them, as their largest diameter has not seemed 

 to be more than from l-20000th to l-14000th 

 of an inch ; and the smallest not more than 

 from l-60000th to l-40000th. 



The nature and fancied uses of marrow and 

 oil of bones will be considered elsewhere. 



The bones, periosteum, and marrow are, in 

 the sound state, amongst the insensible parts of 

 the frame. They are certainly not sensible to 

 ordinary irritants ; but, when morbid, exhibit 

 intense sensibility. This applies, at least, to 

 bones and the periosteum ; the sensibility, which 

 has been ascribed to the marrow, in disease, 

 being probably owing to that of the prolonga- 

 tions of the membrane in which it is contained. 



Fig. 164. 



Fig. 163. 



Haversian Canals, seen on a 

 Longitudinal Section of the 

 Compact Tissue of the Shaft 

 of one of the Long Bones. 



1. Arterial canal. 2. Venous 

 canal. 3. Dilatation of another 

 venous canal. 



Transverse Section of Compact Tissue of Humerus magnified about 150 diameters. 



Three of the Haversian canals are seen, with their concentric rings; also the corpuscles or lacunas, 

 With the canaliculi extending from them across the direction of the lamellae. The Haversian apertures 

 had got filled with debris in grinding down the section, and therefore appear black in the figure, which 

 represents the object as viewed with transmitted light. 



The number of the bones in the body is usually estimated at two 

 hundred and forty, exclusive of the sesamoid, which are always found 



