GENERAL HISTOLOGY 



77 



Cartilage. — Cartilage and bone are likewise tissues whicti 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 pericjimidrium — 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 (cliondrin) 

 by cooking produces a kind of glue which 

 differs from true or glutin glue in that it 

 is precipitated by acetic acid. The car- 

 tilage cells lie in the matrix united in 

 groups and nests, a mode of grouping 

 pointing to their origin, since each group 

 has arisen from a single mother-cell by 

 successive divisions. In cartilage also, 

 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 

 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 

 \\ith 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 

 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 bmte lamella- (fig. 45), 

 whose arrangement is determined by 



the surfaces present in and on the bone. In a hollow bone (like that of the 

 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 Haversian 

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

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





Fig. 45. — Cross-section through the 

 human metacarpus (after Frey). a, 

 surface of the periosteum; 6, surface 

 of the marrow-canty; c, cross-sections 

 of the Haversian canals and their 

 system of laraellas; d, fundamental 

 lamelke; e, bone corpuscles. 



