ANATOMY OF VERTEBRATES. 



21 



§ 11. Dcvclopement of hone. — The primitive basis, or ' l)liis- 

 tema,' of bone is a sul)transparent glairy matter containing 

 numcrons minute corpuscles. It progressively 9 



acquires increased firaniess; sometimes assuming 

 a membranous or ligamentous state, usually 

 a gristly consistence, before its conversion into 

 bone. The change into cartilage is noted b}^ 

 the a|)pcarance of minute nucleated cells ; which 

 increase in number and size, and are a<iiire<i-ated 

 in rows, with intercellular tracts, where the ossi- 

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

 rows, in the cartilaginous basis ol' long bones, 

 are vertical to its ends : in that of fiat bones 



, -11 • mi Section of temponiry cai-tl- 



they are vertical to the margm. The cells I'lsc, iviiicn bas umingono 



,-.",,, , f, •? ,• a , the last sl;igo towards ossl- 



tin-tncst trom the seat ot ossifacation are flat- tkation. cl. 

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

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

 tissue ; h the enlarged cell- wall ; e 

 the nucleus. The first appearance 

 of bone is that of minute granules 

 in tlie intercolmnnar and intercellu- 

 lar tissue, fig. 10, II. Canals are 

 next formed in the bone, liy absorp- 

 tion, which ultimately receive blood- 

 vessels, and become the ' vascular 

 canals.' The immediate nutrition of 

 Ijone is provided for by the produc- 

 tion of minute ' plasmatic canals ' 

 fi'om 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 11 ; where 

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

 ' jdasmatic 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-l)ream ( Siirf/us) 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 Pi/tlwn, they are commonly, where best defined, 

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

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

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

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

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



of temporary cartilage 

 of os.^iDcation. ci^. 



