ANATOMY OF VERTEBRATES. 



21 



§ 11. Devehpement of bone. — The primitive basis, or 'blas- 

 tema,' of bone is a subtransparent glairy matter containing 

 numerous minute corpuscles. It progressively 9 



acquires increased firmness ; sometimes assuming 

 a membranous or ligamentous state, usually 

 a gristly consistence, before its conversion into 

 bone. The change into cartilage is noted by 

 the appearance of minute nucleated cells ; which 

 increase in number and size, and are aggregated 

 in rows, with intercellular tracts, where the ossi- 

 fication is about to begin, as in fig. 9. These 

 rows, in the cartilaginous ba 

 are vertical to its ends ; 

 they are vertical to the 



- — j — — ~p- 



>asis of long bones, 

 in that of flat bones 



Section of temporary carti- 



margill. The Cells Ia se. which has undergone 



. ~ the last stage towards ossi- 



iurthest from the seat 01 ossification are flat- fication. ol. 

 tened and in close contact ; nearest that seat they become enlarged 

 and separated. In fig. 9, a is the intercellular or ' intercolumnar ' 

 tissue ; b the enlarged cell-wall ; c 

 the nucleus. The first appearance 

 of bone is that of minute granules 

 in the intercolumnar and intercellu- 

 lar tissue, fig. 10, a. Canals are 

 next formed in the bone, by absorp- 

 tion, which ultimatelv receive blood- 

 vessels, and become the ' vascular 

 canals.' The immediate nutrition of 

 bone is provided for by the produc- 

 tion Of minute ' plasmatic Canals ' Transverse section of temporary cartilage in 

 „ . . the first stage of ossification, cl. 



irom the vascular ones. 



In most fishes the plasmatic canals are free from partial dilata- 

 tions, and appear as in the magnified section of bone, fig 1 1 ; where 

 a shows the area of the ' vascular canal,' and b the orifices of the 

 ' plasmatic canals,' exposed in a longitudinal section of a vascular 

 canal. In some fishes, e. g. the Garpike (Belone), partial dilatations 

 do occur in the plasmatic canals, of the form shown in fig. 12, d; and 

 in a Sea-bream (Sargas) of that marked c ; in the Frog they are 

 wider and more defined, as in the two dilatations shown at a. In 

 serpents, e. g. the Python, they are commonly, where best defined, 

 of the elongate oval form shown in 1, 2, and 3, fig. 13 ; but in 

 transverse section they appear as in 5 and 6. In the bird, e. g. 

 the Goldfinch, they have the form shown in b, fig. 12. In human 

 bone they assume the forms represented in fig. 14. When so 

 defined they are termed ' lacuna3 ' or i bone-cells ; ' and, in some 



