106 PRACTICAL HISTOLOGY. 



a good plan to replace the water in which the strips 

 are mounted by glycerine, since this renders the tex- 

 ture too transparent and the outlines too indefinite. 

 But the strips may be mounted and preserved for a 

 considerable time in water merely if the edges of the 

 cover-glass are fixed first by melted paraffin, and then 

 by layer after layer of chloroform balsam, so as to 

 obviate as much as may be the risk of evaporation. 



The bones in which the fibres of Sharpey may best be 

 demonstrated in the way above described are the flat 

 bones of the skull. They are also to be seen in similar 

 preparations, and in sections of the long bones. If a sec- 

 tion be made of such a bone at the place of insertion into 

 it of a tendon or ligament, and in the direction of the fibres 

 of the tendon or ligament, it will be seen that the bundles 

 of fibres of the last-named structures are continued into 

 the substance of the bone as perforating fibres or fibres of 

 Sharpey, so that these in fact almost compose the whole of 

 the osseous tissue at this place (Ranvier). This shows, 

 moreover, that the fibres of Sharpey are to be regarded as 

 bundles of fibrous tissue (connected either with the perios- 

 teum or with a tendon or ligament) which were intercalated 

 with the osseous substance proper when this was formed 

 and have become ossified at the same time. When tendons 

 undergo ossification, the bony substance which is formed 

 is wholly of the same nature as the fibres of Sharpey; 

 this may be characteristically seen in the ossified tendons 

 which are met with in the legs of birds. 



Preparation 7. Development of bone in 

 membrane. For the study of the intra-membra- 

 nous process of .ossification it is best to employ the 

 flat bones of the skull of sheep's embryos from two 

 to three inches long. The embryos may have been 

 preserved in Muller's fluid, 1 or spirit, or they may 

 be employed fresh. A piece (corresponding in posi- 

 tion with the future parietal, for example) of the 

 still membranous skull-cap is cut out with fine scis- 

 sors, placed under water if from Muller's fluid, under 



1 A solution containing 2 parts bichromate of potash, and 1 

 part sulphate of soda, to 100 of water. 



