262 



BONE OR OSSEOUS TISSUE. 



uncalcified fibres are by no means frequent (Sharpey). The perforating fibres are 

 often connected with the periosteum, as is the case with most of those which 

 penetrate the external table of the cranial bones ; but in cross sections of cylin- 

 drical bones they often appear to spring with their broad ends from the deeper 

 lamellae (with the fibres of which they may be directly continuous), and especially 

 from those near the circumference of a Haversian system, and taper outwards into 

 fine points, which do not reach the periosteum (fig. 303), although without doubt 

 they must, like the bony layers in which they occur, have been formed by sub- 

 periosteal ossification. They are never found in the concentric systems of Haversian 



Fig. 303. TRANSVERSE SECTION OF DECALCIFIED HUMAN TIBIA, FROM NEAR THE SURFACE OF THE 



SHAFT (K. A. S.). 



H, H, Haversian canals, with their systems of concentric lamellae ; in all the rest of the figure the 

 lamellae are circumferential. 



s, ordinary perforating fibres of Sharpey ; e, e, elastic perforating fibres. Drawn under a power of 

 about 150 diameters. 



lamellae. Perforating fibres exist abundantly in the crusta petrosa of the teeth 

 (Sharpey). 



Where tendons or ligaments are inserted into bone, the fibre-bundles of the 

 tendon are continued into the bone as perforating fibres, so that the attachment of 

 tendon to bone is thus rendered very intimate. Some of the bundles of white 

 fibres of the periosteum may also, as above mentioned, pass into the bone as per- 

 forating fibres, and the same is the case with the elastic fibres. 



The animal basis of bone is made up essentially, as we have seen, of lamellae 

 composed of fine decussating or reticular fibril-bundles embedded in a ground- 

 substance ; but interposed among these lamellae, layers are here and there met with 

 of a different character, having a granular aspect, with the lacunae very conspicuous 

 and regularly arranged, and sometimes appearing as if surrounded by faintly defined 

 areolaa. These generally incomplete layers are often bounded by a scalloped border, 

 as if made up of confluent round or oval bodies ; this is indicated also by the occa- 



