STUUCTUEE. 80 



Jliillei's explanation : at the same time it is equally certain that uncalcified fibres, 

 though numerous at particular spots, are by no means so frequent as might be 

 infeiTed from Mllller's account of them, and that the i^erforating fibres may be 

 said to be generally calcified. Finally, these fibres seem to have no physiological 

 significance : they may be regarded as merely a modification of the mechanical 

 stiaictui'e of the tissue. 



In a thin transverse section of hard bone, the concentric lines, or rather bands 

 which represent the cut edges of the lamelUi^. generally present, with transmitted 

 light, a dark granular-looking, and a light, transparent, and usually narrower 

 zone. Under a liigh power of the microscope the former api^ears thickly dotted 

 over with fine dark points. In a decalcified section the dark part sliows a 

 multitude of short bright lines running radially across it, with dark angular 

 particles between them. Tlie lines are probably caused by pores and fine clefts 

 passing through the lamella ; the appearance of dark iiai-ticles seems to he pro- 

 duced by the cut ends of the reticulating fibres of wliich the lamellaj are made 

 wp. A longitudinal section of a cylindrical bone canied across the lamellai pre- 

 sents a coiTesponding appearance, for as the fibres run more or less oljliquely to 

 the axis of the bone, they present cut ends in a longitudinal section also. 



It thus appears that the animal basis of bone is made up of lamellaj 

 composed of fine reticuhn- fibres ; but interposed among these lamellae, 

 layers are here and there met with of a different character, yiz. : — 



1. Strata of amoiphous or granular aspect, in which the lacunaa are very con- 

 spicuous and regularly an-anged. and sometimes appearing as if surrounded by 

 faintly defined areolae. These generally incomplete layers are often bounded by a 

 scalloped border, as if made up of confluent round or oval bodies ; this is indi- 

 cated also by the occasional occurrence of oval or flattened siiheroidal bodies 

 singly or in small groups near the border of these layers, each with a cavity in 

 the centre. In fact, if the round bodies sho'mi in figure '>?> had a central cavity, 

 they would very -well represent the objects here referred to. In some parts the 

 graiTular substance is obscurely fibrous, and transitions nray be observed to the 

 well-marked reticular laminre. Tlie layers described appear principally to occur 

 near the surface of tlie compact tissue, and at the cii'cumference of many of the 

 systems of concentric Haversian lamella. 



2. Irregular la^-ers of rounded bodies, apparently solid and without central 

 cavity or mark, well represented in figure oo. whicli is after a drawing from 

 nature hy Dr. A. Tliomson. These layers are met with chiefly near the surface of 

 tlie shaft of long bones, lying among the circumferential laminaj, and apparently 

 forming only part of a circuit. They can occasionallj^ be recognised in a trans- 

 verse section as short curvilinear bands of peculiar aspect, bi-oader in the middle 

 and thinning away at the ends, appearing here and there between the cut edges 

 of two ordinary circumferential lamina}. 



The appearances described under 1 and 2, and especially the last, as represented 

 in fig. 53. may be accomited for by the explanation offered by Professor C. 

 Loven, of Stockholm, on seeing the figui'e and specimens ; viz.. that the sur- 

 face covered apparently with globular bodies, single or in botryoidal groups, 

 is really a cast in relief from a contiguous surface of bone that has been 

 excavated by absorjition. It is known that in the gi'owth of a bone absoi-ption 

 occurs at various parts, and is often followed by fresh ossific deposition ; as, for 

 example, in the excavation and subsequent filling u^) of the Haversian spaces. 

 The absoiiition in such cases is a healthy process, but the absorbed surface is. as 

 in absolution from disease, eroded or scooped out into sinuous hollows, the lai'ger 

 of -which are again carved on the inside into smaller rounded pits (foveoloB). New 

 osseous matter deposited on such a sm-face fills up its hollows, and. wlien the 

 new layer is detached, it exliibits a raised impression corresponding with them.* 



* Two olissrvatious -which I have had occasion to make favour this explanation. A 

 cross section of a (large) serpent's rib shows an outer and an inner series of concentric 

 lamellai sun-ounding the medullary canal, and the inner trenches on the outer by a festooned 



