70 NORMAL HISTOLOGY. 



parts of the same piece of cartilage. The reticulum is usually 

 more open and composed of larger fibres toward the centre of the 

 tissue than at the periphery, where it becomes more delicate and 

 finally blends with the fibrous intercellular substance of the peri- 

 chondrium. 



It is evident, both from the structure of the cartilages and from 

 the situations in which they are found, that they constitute elastic 

 tissues suitable for diminishing the effects of mechanical shock. 

 This is obviously the case in the joints, where both the hyaline 

 and the fibrous varieties are found. Their elasticity and moderately 

 firm consistency are also of obvious utility in the larynx and other 

 air-passages and in the ear, nose, and synchondroses. 



II. BONE. 



General Characters. — (1) The cells of bone, called " bone-corpus- 

 cles," have an oval vesicular nucleus, surrounded by a moderate 

 amount of cytoplasm, which is prolonged into delicate branching 

 processes that join those of neighboring cells. (2) The intercellular 

 substance is composed of an intimate association of an organic 

 substance and salts of the earthy metals. (3) The arrangement 

 of these constituents is as follows : the organic basis of the inter- 

 cellular substance is arranged in laminae, which are closely applied 

 to each other except at certain points where there are cavities, called 

 " lacunae," giving lodgement to the bone-corpuscles. Joining these 

 lacunse with each other are minute channels in the intercellular 

 substances, " canaliculi," which are occupied by the fine processes 

 of the corpuscles. In the compact portions of the long bones, and 

 wherever the osseous tissue is abundant, the laminae are arranged 

 concentrically around nutrient canals, the " Haversian canals," 

 which traverse the bone, anastomosing with each other and contain- 

 ing the nutrient bloodvessels of the tissue. In cancellated bone 

 these Haversian canals are absent, and the thin plates of bone are 

 made up of parallel laminae of intercellular substance, between 

 which are the lacunse, connected with each other by canaliculi. The 

 bone-corpuscles are nourished from the fluids circulating in the 

 marrow, which occupies the large spaces of this spongy variety of 

 bone. 



It is not possible in a single preparation to study even these gen- 

 eral characters of bone. The earthy salts in the intercellular sub- 



