MINUTE STRUCTURE OF BONE. 



261 



the deposit of calcareous matter being confined to the matrix in which they are embedded. 

 They appear to be united into the lamellas by a matrix or ground-substance, and take different 

 directions in successive lamellae, so as to produce a granular or a striated appearance according 

 as they happen to be cut transversely or longitudinally (fig. 301). 



In thin sections of bone, the concentric lines or rather bands which represent the cut edges 

 of the lamellas show the section of the decussating fibres as round or angular dots, themselves 

 punctated, which lie embedded in the homogeneous ground-substance (fig. 301, 6). The 

 lamellae are separated from one another by the lacunas which lie between them, where these 

 are absent they are joined together by the ground-substance ; they are also united by 

 occasional bundles of fibres passing obliquely from one lamella to the other. 



Perforating fibres. It was further shown by Sharpey that in many instances 

 the lamellae are perforated by fibres, which pass through them in a perpendicular 

 or oblique direction, and, as it were, bolt them together. These perforating fibres 

 may be seen, with the aid of the microscope, in a thin transverse slice of a decalcified 

 cylindrical or cranial bone, on pulling asunder the sections of the lamellae (as in 

 fig. 304). In this way some lamellae will generally be observed with fibrous pro- 



Fig. 302. LAMELLA TORN OFF FROM A DECALCIFIED HUMAN PARIETAL BONE AT SOME DEPTH FROM 



THE SURFACE (Sharpey). 



a, lamellae, showing decussating fibres ; &, b, thicker part, where several lamellae are superposed ; 

 c, c, perforating fibres. Apertures through which perforating fibres had passed, are seen especially in the 

 lower part, a, a, of the figure. Magnitude as seen under a power of 200, but not drawn to a scale (from 

 a drawing by Allen Thomson). 



cesses attached to them (fig. 304, J) of various lengths, and usually tapering and 

 pointed at their free extremities, but sometimes truncated probably from having 

 been divided by the knife. These fibres have obviously been drawn out from the 

 adjacent lamellae, through several of which they must have penetrated. Sometimes, 

 indeed, indications of perforations may be recognized in the part of the section of 

 bone from which the fibres have been pulled out (fig. 304, c). The processes in 

 question are thus, so to speak, viewed in profile ; but they may frequently also be 

 seen on the flat surface of detached lamellae (fig. 302), projecting like nails driven 

 perpendicularly. 



The perforating fibres are, like the decussating fibres, for the most part bundles 

 of fibrils which agree in character with those of the white fibrous tissue ; but some, 

 as shown by H. Miiller, are of the nature of elastic tissue (fig. 303, e). In some 

 parts they escape calcification, and thus, as they shrink in drying, leave tubes or 

 channels in the dry bone, generally leading from the surface inwardly ; but these 



