10 



OSTEOLOGY, 







are several concentric osseous layers, the j7^?'ij97ie7Y<Z or periosteal 

 lameUce, passing completely round the shaft. There is also a 

 corresponding concentric disposition of layers on the inner or 

 medullary surface. Both these systems 

 of lamella? are in a great measure 

 destitute of Haversian canals, and are 

 supplied with nutritive material by 

 means of lacunse and canaliculi, disposed 

 as in the compact tissue generally. 



The average diameter of the canaliculi 



is ToVoth of an inch. The lacunae are 



somewhat oval, and lie with their long 



diameters, which measure about TsVcrth 



of an inch, parallel to the lamella? ; their 



short diameter is about ueVirth of an 



Longitudinal section of osseous inch. The compact tissuo is therefore 



IIThV.';!';';.;,'!"""''"""*"' copiously supplied with uufimont by 



means of minute vessels, which enter 



from almost every conceivable point. Each Haversian canal 



may be considered a vascular 

 longitudinal centre, round which 

 successive concentric layers of 

 bone are arranged, so as to form 

 a dense cylindrical ossicle, a 

 Haversian System or Cylinder. 

 Series of these are repeated, and 

 Cavity of United by lamella? destitute of 

 canals, but with numerous cana- 

 liculi and lacunae, and called the 

 connecting or interstitial lamelloi, the entire structure being 

 encircled by the external peripheral lamella?, thus constituting 

 the compact tissue, and in such a way as to combine strength 

 and density with efficient nutrition, the nutritive material being 

 conveyed by the canals, canaliculi, and lacunae ; the last two only 

 transmit the fluid portion of the blood. The canaliculi interlace, 

 and some pass directly through the lamellae to the central 

 Haversian canal. The lamellae are in places pierced, and, as it 

 were, pinned together by fibres, or fibrous bundles known as the 

 perforating fibres of Sharjjey; some of these are derived from the 

 periosteum, and some even appear to be continued from inserted 

 tendons and ligaments. 



Flo. 4. 

 Lacunae liiglily magnifled. 

 lacuna ; h h, The canaliculi ; those of the two 

 lacunae on the left are seen to join each other. 



