260 



BONE OR OSSEOUS TISSUE. 



depth in a straight or crooked direction through the leaves of a book, in which case 

 it is plain that the perforations of the adjoining leaves would correspond ; it being 

 understood, however, that the passages thus formed are most likely bounded by 

 proper parietes. The apertures now referred to must be distinguished from larger 

 holes seen in some lamellae, which give passage to the perforating fibres to be 

 mentioned further on. 



But the lamellse have a further structure. To see this, the thinnest part of a 

 detached shred or film must be examined, as shown in figs. 300 and 302 ; it will 

 then appear plainly that they are largely made up of transparent fibres, decussating 

 with each other in the form of an exceedingly fine network. In the Haversian 

 systems these decussating fibres cross one another in different lamellse at right 

 angles (v. Ebner), but in most other situations at more or less acute angles, and 

 they are united here and there by obliquely passing fibres, so that they cannot be 

 teased out from one another ; but at the torn edge of the lamella they may often be 

 seen separate for a little way, standing out like the threads of a fringe. Most 

 generally they are straight, as represented in fig. 300 ; but they are not always so ; 

 for in some parts they assume a curvilinear direction (fig. 302). Acetic or hydro- 



Fig. 300. THIN LAYER PEELED OFF FROM A SOFTENED BONE, AS IT APPEARS UNDER A MAGNIFYING 

 POWER OF 400 DIAMETERS (Sharpey). 



This figure, which is intended to represent the reticular structure of a lamella, gives a better idea of 

 the object when held rather farther off than usual from the eye. 



Fig. 301. SMALL PART OF A LONGITUDINAL SECTION OF DECALCIFIED TIBIA. HIGHLY MAGNIFIED (after 



v. Ebner). 



a, series of six lamellae which are cut for the most part in the direction of the fibrils, so that they 

 appear longitudinally striated ; b, b, lamellae, the fibrils of which are cut across ; the arrangement of the 

 fibrils into bundles is indicated. Two lacunae are seen lying between the lamellae, also canaliculi piercing 

 the lamellse. 



chloric acid causes these fibres to swell up and become indistinct, like the white 

 fibres of connective tissue ; care must therefore be taken in their examination that the 

 remains of the decalcifying acid be removed from the tissue, by maceration in water 

 or in solutions of neutral salts. Moreover, the fibro-reticular structure is not equally 

 distinct in all parts ; for in some places it is less decidedly marked, as if the fibrilla- 

 tion were incompletely developed. 



The decussating fibres which constitute the lamellse were discovered by Sharpey, and their 

 constant presence was taught by him for a long time before they were admitted by other 

 histologists. It has lately been shown by v. Ebner that the decussating fibres of Sharpey are 

 in reality themselves composed of exquisitely fine fibrils, so that they correspond with bundles 

 of white connective tissue fibres rather than with single fibres. Like the connective tissue 

 fibrils these of the bone are doubly refracting, and they are said (Ebner) not to be calcified. 



