ON THE STRUCTURE AND DEVELOPMENT OF BONE. 143 



years engaged in the practice of his profession, Troja resumed 

 his early work, and in 1814 published a quarto volume, entitled 

 * Osservazioni ed Esperimenti sulle Ossa, in Supplemento ad un 

 Opera sulla Eigenerazione delle Ossa, impressa nel 1775 e nel 

 1779/ This volume contains the results of further inquiries on 

 the reparation of bone and observations on various diseases of 

 the osseous system, with finely executed figures, preceded by an 

 account of the intimate structure of bone in general, as studied 

 in the growing bones of the foetal cranium at diflVrent stages, 

 and in adult bones decalcified by means of phosphoric or nitric 

 acid; but no figures are given in explanation of the author's 

 histological descriptions. 



Although aware that his distinguished countryman, Scarpa, 

 denied the lamellar structure of bone, Troja maintained its 

 reality as generally understood by preceding and contemporary 

 anatomists, inasmuch as he could split the compact tissue, after 

 decalcification, into layers — " piani fibrosi^' — of greater or less 

 thickness, but not identical with the fine lamellae since recog- 

 nised. The layers he describes as made up of fibrous bundles, 

 which he distinguishes into two orders — first, those of larger size 

 " fasci fibrosi di prim' ordine'' — which run longitudinally in some 

 bones, as the tibia, or radially, as in those of the calvaria, where 

 they form meshes by oblique lateral junction and by lateral off- 

 sets, " appendici,'' an appearance especially well seen in the 

 fcBtal head ; and, secondly, finer bundles — " fascetti fibrosi di 

 second' ordine." These last cross the larger bundles in the same 

 plane or dip down into deeper strata, an arrangement which he 

 compares to the warp and woof of a web, and describes as visible 

 in the growing parietal of a foetus of three months, in which the 

 larger bundles appear as if encircled by fine transparent rings 

 formed by those of the second order. Clementi considers these 

 to be undoubtedly the perforating fibres, but to me this is by no 

 means clear. On the other hand, I cannot doubt that Troja did 

 truly recognise the perforating fibres, for he makes unequivocal 

 reference to them in the account he gives (p. 37) of the bands — 

 " legamenti'^ — by which the difl'erent layers are held together. 

 He explains that the different fibrous bundles already described 

 not only join each other laterally in the same layer, but serve to 

 bind together different layers, and thus describes the arrange- 

 ment. In forcing asunder, he says, with the aid of a probe 

 flattened at one end, the concentric layers in a softened bone, the 

 offsets or appendices of the large fasciculi are seen crossing the 

 probe, and on introducing a finger between a partially detached 

 layer and the bone to which it belongs these appendices, still 

 entire, are seen passing from one surface to the other, but on 

 lurther pressure with the probe they break across with a faint 



