COMPOSITION AND DEVELOPMENT OF BONE. 167 



It will be observed that, in all cases, the proportion between the cartilaginous basis and 

 the earthy matter is very nearly the same ; being almost exactly as 1 to 2, even where the 

 composition of the bone is most altered, by the presence of an unusual quantity of fatty mat- 

 ter. Hence there is strong reason to believe, that a definite chemical compound is formed 

 by the union of the Gelatine and Earthy salts ; and this corresponds well with the fact 

 already noticed, in regard to the homogeneousness of the ultimate particles of bone. 



197. The first Development of Bone may take place in the substance, 

 either of Membrane, or of Cartilage.* The tabular bones forming the roof 

 of the cranium afford a good example of the first, or intramembranous form 

 of Ossification : for their place is but in part pre-occupied by cartilage ; only 

 a membrane being elsewhere interposed between the dura mater and the in- 

 teguments. This membrane is chiefly composed of fibrous fasciculi, corre- 

 sponding with those of the white fibrous tissues ; but amongst these are seen 

 numerous cells, some about the size of blood-discs, but others two or three 

 times larger, containing granular matter ; and a soft amorphous or faintly- 

 granular matter is also found interposed amidst the fibres and cells. In cer- 

 tain parts, the fibres predominate ; and in others, the cells. The process of ossi- 

 fication here seems at first to consist in the consolidation of the fibres by earthy 

 matter ; for the first bony deposit consists of an irregular reticulation, very loose 

 and open towards its edges, and there frequently presenting itself in the form 

 of distinct spicula, which are continuous with fasciculi of fibres in the sur- 

 rounding membrane. The limits of the calcifying deposit may be traced by 

 the opaque and granular character of the parts affected by it, and it gradually 

 extends itself, involving more and more of the surrounding membrane, until the 

 foundation is laid for the entire bone. Everywhere the part most recently 

 formed consists of a very open reticulation of fibro-calcareous spicula ; whilst 

 the older part is rendered harder and more compact, by the increase in the 

 number of these spicula, and perhaps also by the calcification of the interve- 

 ning cells. As the process advances, and the plate of bone thickens, a series 

 of grooves or furrows, radiating from the ossifying centre, are found upon its 

 surface ; and these by a further increase in thick ness, occasioned by a deposit 

 of ossific matter all around them, are gradually converted into closed canals 

 (the Haversian), which contain blood-vessels, supported by processes of the 

 investing membrane. Further deposits subsequently take place in the interior 

 of these canals ; which thus gratlually produce a diminution of their calibre, 

 and a consolidation of the bone ; and in this manner its two surfaces acquire 

 their peculiar density, whilst the intervening layer or diploe retains a charac- 

 ter more resembling that of the original osseous reticulation. The mode in 

 which the peculiar lacunae and canaliculi are formed, in the concentric layers 

 around the Haversian canals, probably corresponds with that in which they 

 are generated in the intracartilaginous form of ossification, to which we shall 

 next proceed. 



198. In a very large proportion of the skeleton, the appearance of the Bones 

 is preceded by that of Cartilages ; which present the same form, and which 

 seem destined to afford a certain degree of support, to the surrounding soft 

 parts, until the production of Bone has taken place. As already mentioned 

 ( 187), the temporary cartilages differ in no essential particular from the/>er- 

 manent. They present the same irregular scattering of cells through a homo- 

 geneous intercellular substance, and there is the same absence of any vascu- 



* In recent times, the development of Bone from Cartilage has received almost exclusive 

 attention ; but the older opinion, that Bone is often developed in Membrane, has been lately 

 brought again into notice by Dr. Sharpey (Introduction to Fifth Edition of Quain's Anatomy), 

 who has demonstrated its truth by Microscopic research. The statements in the text, upon 

 this part of the subject, are derived from Dr. Sharpey's observations, which the author has 

 since confirmed. 



