5i8 



THE CELL AND MAMMALIAN HISTOLOGY 



in the pinna or external ear trumpet. Cartilage is sometimes 

 hardened by the deposition in it of calcium salts, when it is 

 said to be calcified. 



BONE 



Bone contains cells called osteocytes, but its most striking 

 feature is the fibrous and collagenous ground substance im- 

 pregnated with complex calcium salts, largely phosphate. The 



J l_ "ftOu-jcRo 



Fig. 403. — Section of adult bone (human femur). — From Le Gros Clark. The 

 Tissues of the Body, 3rd edition, 1952. Clarendon Press, Oxford. 



He, Haversian canal ; Int., interstitial lamellae ; Lac., Lacunae, x c. 150. 



fibres are arranged in lamellae, and a transverse section of a hard 

 bone shows that these form many-layered tubes called Haversian 

 systems (Figs. 403 and 404). Between these and round the edge 

 of the bone the lamellae are irregular. The Haversian canal 

 which runs down the centre of each system contains an artery, 

 a vein, and a nerve, and some reticular tissue (p. 526). It branches 

 and joins other canals, and some of these open into the space, 

 if there is one, in the bone, which contains bone marrow (p. 526). 

 The osteocytes are situated in spaces or lacunae between the 

 lamellae ; these lacunae communicate with each other, and with 



