GENERAL HISTOLOGY 



77 



Cartilage. Cartilage and bone are likewise tissues which find their charac- 

 teristic development only in the vertebrates. In appearance cartilage is similar 

 to the homogeneous connective tissue of many invertebrates; the matrix is 

 homogeneous and, at first glance, appears structureless (fig. 44), but, under the 

 action of certain reagents, assumes a fibrous condition. This, as well as the 

 fact that the cartilage grows through 

 changes of the perichondrium a thin, 

 fibrillar membrane covering its surface- 

 makes it more evident that it is homo- 

 geneously fibrillar; and it is thereby dis- 

 tinguished from homogeneous connective 

 tissue since it is not, like the latter, a 

 lower but a higher stage of tissue forma- 

 tion. The matrix of cartilage (chc.ndrin} 

 by cooking produces a kind of glue which 

 differs from true or glulin glue in that it 

 is precipitated by acetic acid. The car- 

 tilage cells lie in the matrix united in 

 groups and nests, a mods of grouping 

 pointing to their origin, since each group 

 has arisen from a single mother-cell by 

 successive divisions. In cartilage also, c 

 elastic fibres are found; if present in great 

 number, these change the bluish, shiny, 

 hyaline cartilage into the yellow-colored 

 elastic cartilage. 



The 'head cartilages' of the cepha- 

 lopoda differ from vertebrate cartilage 

 in that the cartilage corpuscles have e 

 branched processes. 



Bone is the most complicated struc- 

 ture in the series of connective tissues. 

 It consists of a matrix (ossein), closely 

 allied to glutin, so intimately combined 

 with inorganic constituents that it appears 

 under the microscope as a homogeneous 

 mass. The proportion of organic and 

 inorganic substances varies according to 

 the age and species of animal: in man 

 there is 65% inorganic to 35% organic 



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substance; in the turtle, 63% to 37' , 

 Of the inorganic constituents, the most 

 important is calcic phosphate, 84'^; in 

 smaller quantities, combinations of 

 fluorine, chlorine, carbonic acid and mag- 

 nesia. In compact bone the matrix is 

 composed of the bone lamella: (fig. 45), 

 whose arrangement is determined by 



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FIG. 45. Cross-section through the 

 human metacarpus (after Frey). </. 

 surface of the periosteum; b, surface 

 of the marrow-cavity; c, cross-sections 

 of the Haversian canals and their 

 system of lamella;; d, fundamental 

 lamella?; c, bone corpuscles. 



In a hollow bone (like that of the 



the surfaces present in and on the bone. 



upper arm) there is an outer surface to which a fibrous membrane, the 

 periosteum, is closely applied; the presence of the marrow-cavity necessitates a 

 second surface. Finally, the mass of the bone is permeated by the Haversi< 

 canals, which run chiefly in a longitudinal direction, united by cross or oblique 

 canals, and serve for the passage of blood-vessels. Since the bone lamellae 



