STRUCTURE OF BONE. 



87 



tered in other forms of dense connective tissue. Since the lacunae are compressed 

 oval cavities lying between the lamellae of the osseous matrix, when viewed in sec- 

 tions which pass through the layers at right angles (Fig. 117), the lacunae present 

 their narrower dimensions, appearing thus in profile as small lentiform spaces ; seen 

 in sections, on the contrary, which pass parallel to the lamellae (Fig. 118), the 

 lacunae are broader and more circular, the spaces with the canaliculi forming the 

 spider-like figures so conspicuous in longitudinal sections of dried bone. 



The characteristic arrangement of the lamellae of the Haversian systems is due 

 to the secondary formation of the osseous tissue during the conversion of the older 

 spongy bone into compact tissue, the circumference of the system corresponding to 

 the Haversian space in which the subsequent development of the concentric lamellae 



Fig. 115. 



Circumferential 

 lamellas 



Interstitial lamellas 



Haversian canal 



iljj' 'Obliquely cut Haver- 

 tii't! sian canal 



Longitudinal section of compact bone, ground and dried. X 85. 



took place. It follows, from this relation, that Haversian systems exist only in com- 

 pact bone, since the necessary secondary deposit does not occur during the growth 

 of the spongy or cancellous tissue. 



The lamellae of osseous tissue, when deprived of the mineral matters and exam- 

 ined in thin fragments, often display the ultimate fibrous structure which they pos- 

 sess, since they consist of delicate fibrils oi fibrotis tissue embedded within a ground- 

 substance and associated into bundles which are arranged as crossing and interwoven 

 layers. Within the Haversian lamellae the fibrous bundles cross generally at right 

 angles, but in other locations they are less regularly and more acutely disposed. 



The perforating fibres of Sharpey (Fig. 119) consist of bundles of fibrous 

 tissue which penetrate the lamellae in a direction perpendicular or oblique to their 



