I04 



CHORDATE ANATOMY 



Bone. Cartilage and bone are similar in that their essential skeletal 

 material is a non-living matrix within which are imbedded living cells. 

 Bone differs from cartilage in that the matrix is highly calcified and cor- 

 respondingly hard and also in that it never exhibits the apparent homo- 

 geneity of the matrix of hyaline cartilage but is disposed in very thin 



-'BLOOD VESSEL 



^COMPACT BONE 



^MARROW 



ARTICULAR UGAMENT 



Fig. 100. — Diagram of the structure of a long bone. (Redrawn from Kahn's " Der 

 Mensch," Albert Miiller, Zurich.) 



parallel layers. Usually the deeper substance of a bone (Fig. loo) is of a 

 porous or spongy texture (cancellous bone) while the outer region is 

 dense or solid (compact bone). 



A section of fully developed compact bone, seen under high magnifica- 

 tion, shows the matrix layers or lamellae arranged in parallel or concentric 

 order (Fig. loiB and 102). Between adjacent lamellae are minute 



Fig. loi.- — A, stereogram representing a sector of the shaft of a long bone. B, 

 transverse section, much more enlarged, showing part of one Haversian system, bl, 

 bone lamellae; c, canaliculi; /;, Haversian canal; I, lacuna. (From Kingsley.) 



cavities, the lacunae. Exceedingly fine canals, the canaliculi, extend 

 between each lacuna and neighboring lacunae, piercing the intervening 

 lamellae. In bone of a living animal each lacuna is occupied by a living 

 bone-cell (osteoblast) from which processes extend into the adjoining 

 canaliculi. 



All external surfaces of bone are covered by a membrane, the perios- 

 teum (Fig. 100), of dense fibrous connective tissue well supplied with 

 blood-vessels which enter the bone and branch throughout it. Most 



