88 BONE. 



or slantingly through a board (fig. 52, c); -whilst the lamellce at 

 other parts present obvious apertures of considerable size, through 

 ■which perforating fibres had passed (as at a). 



These perforating fibres exist very generally in the bones of vertebrata. The 

 late Henry Miiller, of Wurzburg, has sup^^lied many details respecting their 

 arrangement in man and mammalia.* KoUiker considers them to be connected 

 with the periosteum, and this, no doubt, is the case •nith some of them — some of 

 those, for example, which penetrate the external table of the cranial bones : but 

 in cross sections of cylindiical bones they often appear to spring, -nith their broad 

 ends, from the deeper lamellte, and taper outwards into fine points, which do 

 not reach the periosteum ; although -^vithout doubt they must, like the bony 

 layers in which they occur, have been formed by subperiosteal ossification. They 

 are rarely found, and when present are smaller, in the concentric systems of 

 Haversian lamellaB ; in this case they must of course have been formed from 

 the osteoblastic tissue (similar in nature to that under the periosteum) which 

 occupied the medullary spaces and produced the concentric laminse. Perforating 

 fibres exist abundantly in the criista i}etrosa of the teeth. 



Fig. 52.- — Lamell.e torn off from a Decalcified Human Parietal Bone at 



SOME DEPTH FROM THE SURFACE. 



a, a lamella, showing reticular fibres ; &, h, darker part, where several lamellie are 

 superposed; c, c, jicrforating fibres. Ai^ertures through which perforating fibres had 

 passed, are seen especially in the lower jmrt, «, a, of the figure. Magnitude as seen 

 under a power of 200, but not drawn to a scale (from a drawing by Alien Thomson). 



The perforating fibres, or rather bundles of fibres, for the most part agi'ee in 

 character with the white fibrous tissue, but some, according to H. JMliller, are of 

 the nature of elastic tissue. H. IMiiller has shown that in some pai"ts the fibres 

 escape calcification, and thus, as they shrmk in drying, leave tubes or channels 

 in the dry bone, generally leading from the surface inwardly. In this way he 

 explains the nature and mode of production of the '" tubes " described by Tomes 

 and De Morgan as penetrating the bone in certain situations, and conjectured by 

 them to be mothfied lacunaj.f There can be no doubt of the correctness of 



* Wiirzburger Naturw. Zeitschr., vol. i., p. C'JG. 

 t Phil, Trans. 1853, p. 116. 



