156 



COMPARATIVE ANATOMY 



Several types of cartilage are distinguished. Hyaline cartilage (Fig. 

 118), appearing bluish and clear or translucent, has a matrix which is quite 

 or nearly devoid of fibrous material. Fibre -cartilage is, so to speak, a 

 hybrid of cartilage and connective tissue. Its matrix consists partly of 

 hyaline material but largely of fibers similar to those of ordinary connec- 

 tive tissue. Elastic cartilage contains numerous elastic fibers which impart 

 to it a yellowish color and a more or less elastic texture. Calcified 

 cartilage is rendered white and relatively hard by deposit of calcium salts 

 in the matrix. 



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

 material is an intercellular matrix within which are imbedded the cells 

 which produced it. Bone differs from cartilage in that the matrix is 



Fig. 119. — 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; h. Haversian canal; I, lacuna. (From Kingsley.) 



highly calcified and correspondingly. hard and also in that it never exhibits 

 the apparent homogeneity of the matrix of hyahne cartilage but is disposed 

 in very thin parallel layers. Usually the deeper substance of a bone 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 (Figs. 119^ and 120). Between adjacent lamellae are minute cavi- 

 ties, the lacunae. A lacuna is broad in any direction parallel to the surface 

 of a lamella but very thin in the direction perpendicular to that surface. 

 Exceedingly fine canals, the canaliculi, extend between each lacuna and 

 neighboring lacunae, piercing the intervening lamellae. In bone of a 

 hving animal each lacuna is occupied by a living bone cell (osteoblast) 

 from which processes extend into the adjoining canaliculi and may even 

 unite with similar processes from the occupants of neighboring lacunae. 

 It follows, therefore, that the bone is penetrated by a system of continuous 

 spaces and it is probable that in young bone the bone cells, joined by their 

 processes, constitute a continuous network of protoplasm throughout the 

 bone. 



