GERDY ON THE INTIMATE STRUCTURE OF BONE. 25 



numerous, fine, so closely compressed together and so adherent, 

 that their arrangement has escaped the observation of anato- 

 mists. The existence of these vessels in the forming bone is 

 well understood, and they have been injected with mercury by 

 Tiedemann in the parietal bone,* In the adult healthy bone, 

 they are more difficult of detection, in consequence of *the dense 

 nature of the compact substance, in which the vascular chan- 

 nels of the bones and the vascular orifices on the surface are 

 reduced nearly to a microscopical size. But when the bony 

 tissue is diseased or inflamed, as in fractures or after amputa- 

 tions, their existence is no longer doubtful. Blood issues from 

 them when cut, and the vascular orifices on the surface, as 

 well as the canals in the compact tissue are visible to the naked 

 eye, and in some instances are said to have been Fig. l.f 

 as large as a pigeon's quill. Fig. 1, is a view 

 of these canals, as seen in a bone twenty-five 

 days after amputation. When the orifices and 

 canals are thus expanded, the compact tissue 

 appears rarefied, rough on its surface, more 

 light and fragile and corresponds in appearance 

 with the canaliculated tissue of Gerdy. 

 The absence of fibrous appearance on the thick and mixed f 

 bones is dependent upon the direction of the canals, none of 

 which run parallel to the surface, but are all directed towards 

 the articular surfaces of the bones. In the foetus at birth the 

 compact portion of these bones appears sieve-like, from the 

 number of vascular orifices on the surface, which lead perpen- 

 dicularly to the canals that run towards the centre of the bones. 

 Hence, according to Gerdy, the compact layer of these bones, 

 is made up of minute bony rings, surrounding the numerous 



* See Breschet, plates of the Venous System. p. 



f Fig. 1. Section of the extremity of the os femoris, twenty-five days after 

 amputation. It appears cribriform from the number of irregular orifices, be- 

 longing to the canals of Havers (canaliculi,) in. the compact portion of the bone. 

 The vessels which occupy these canals, are greatly enlarged by inflammation. 

 Cases of this sort have been confounded by writers, with inflammation of the 

 veins of the bones. p. 



\ The mixed bones are those which are mixed in their character ; being partly 

 short and partly flat, as, the sacrum, the temporal, maxillary bones, &c. 



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