DEVELOPMENT AND GROWTH OF BONE. 171 



are formed in the same manner as those of the tabular bones of the skull ; the 

 osseous matter being not only laid on in strata parallel to the surface, but also 

 being deposited around processes of the vascular membranous tissue, which 

 extend obliquely from the surface into the substance of the shaft; the canals, 

 in which these membranous processes lie, becoming narrowed by the depo- 

 sition of concentric osseous laminae, and at last remaining as the Haversian 

 canals. Whilst this new deposition is taking place on the exterior of the 

 shaft, absorption of the inner and older layers goes on : so that the central 

 cavity is proportionally enlarged. The increase of the bone in length ap- 

 pears due to the growth of the cartilage between the shaft and the epiphyses, 

 so long as this remains unconsolidated by ossific deposit ; and this state con- 

 tinues, until the bone has acquired nearly its full dimensions. What further 

 increase it gains, seems chiefly if not entirely due to the progressive ossifica- 

 tion of the articular cartilage covering the extremities ; which progressively 

 diminishes in thickness during the whole of life, and which in old age some- 

 times appears to have been almost completely converted into bone. 



202. It thus appears doubtful, whether there be anything like a proper 

 interstitial growth in bone ; that is, whether the part, through which the 

 ossific process has made its way, is capable of any further extension than by 

 addition to its surface. By the. admirable system of prolongations, however, 

 by which the vascular membrane is conveyed into its intimate substance, we 

 rind this method of superficial deposit adapted to the consolidation of parts, at 

 first sketched out (as it were) by a slight osseous reticulation ; whilst by the 

 facility with which the bony matter is absorbed in the internal part of the shaft, 

 whilst it is being deposited upon its exterior, the same effect is produced, as 

 if the whole cylinder could enlarge uniformly by a proper interstitial growth, 

 in the manner of the softer tissues. Much of our information regarding the 

 mode in which new bony matter is deposited, is derived from observations 

 made upon the bones of animals that have been fed with madder ; for this 

 colouring-matter, having a strong affinity for bone-earth, tinges all those parts 

 which are in close relation with the vascular surfaces. In very young ani- 

 mals, a single day serves to colour the entire substance of the bones ; for 

 there is in them no osseous matter far removed from a vascular surface. 

 At a later period, however, the colouring matter is deposited less rapidly ; and 

 is found to be confined to the innermost of the concentric laminae of bone, 

 surrounding each Haversian canal, showing that this is the last formed. 

 When madder is given to a growing animal, the external portion of the bone 

 is first reddened ; showing that the new deposit takes place exclusively in 

 that situation. And if, when time has been allowed for this part to become 

 tinged, the administration of the madder be discontinued, and the animal be 

 killed some weeks afterwards, the red stratum is surrounded by a colourless 

 one of subsequent formation ; whilst the colourless layer internal to the red 

 one, and formed previously to it, is thinned by absorption from within. By 

 alternately administering and withholding the madder, a succession of coloured 

 and colourless cylinders may thus be formed in the shaft of a long bone ; 

 which present themselves as concentric rings in its transverse section. 



203. The nature of the Ossifying process receives some additional light 

 from the abnormal forms in which it occasionally presents itself in Cartilages 

 that are usually permanent ; as well as in various softer tissues, such as the 

 coats of the arteries, fibrous and serous membranes, muscular substance, &c. 

 In these cases, the ossific deposit may often be seen to take place, in the first 

 instance, in the form of distinct granules, which gradually coalesce ; or in the 

 form of spicular fibres, to which additions are progressively made; until a 

 solid mass is produced. This adventitious bone, however, almost invariably 

 differs from true or normal bone, in the want of a regular Haversian system 



