CONNECTIVE TISSUES 17 



protect vital organs in the skull and trunk and acts as levers 

 which are worked by the muscles in the limbs. The tissue is 

 characterized by the deposit of calcareous or lime salts within 

 its intercellular substance, to which its well-known hardness is 

 due. Most bones may be divided into an outer layer of compact 

 bone and an inner layer of spongy or cancellated bone. 



FIG. 15. Transverse section of compact bony tissue (of humerus). 



Three of the Hayersian canals are seen, with their concentric rings; also the lacunae, 

 with the canaliculi extending from them across the direction of the lamellae. The 

 Haversian apertures were filled with air and debris in grinding d9\vn the section, and 

 therefore appear black in the figure, which reoresents the object as viewed with 

 transmitted light. The Haversian systems are so closely nacked in this section that 

 scarcely any interstitial lamellae are visible. X 150. (Kirkes after Sharpey.) 



Microscopically bone is seen to consist of numbers of osseous 

 layers or lamellae, arranged as, (a) circumferential lamella which 

 are arranged parallel to the inner and outer surfaces of the bone, 

 (b) Haversian lamellae which are arranged concentrically around 

 the Haversian canals and (c) interstitial lamellae, which are 

 arranged irregularly so as to fill in the spaces which the other 



