DEVELOPMENT OF BONE. 131 



of the long axis of the bone, superimposed upon one another, 

 so that a transverse section made from this region presents 

 some similarity to that of the free surface of the articular 

 cartilages, or that exhibited by other cartilages in the layer im- 

 mediately beneath the perichondrium. These long rows of flat 

 cells are further characterised by the circumstance that they are 

 often clavate, and intercalate with one another alternately, 

 with their pointed extremities directed in opposite ways.* It 

 is moreover not difficult to convince one's self that these rows of 

 cells originate in continuous processes of fission ; and in regard 

 to this point the preparations are very instructive that were ex- 

 amined and described by Aeby, showing that the club-shaped 

 cells develop from the transverse fission of elongated cells, the 

 daughter cells becoming placed alternately one above the other. 

 The several long rows of flat cells are not all arranged at equal 

 distances from one other, but are divided into variously sized 

 vertical groups by strong trabeculse of the matrix. 



To the well characterised region of flattened cells, arranged 

 in vertical rows, there succeeds near the line of ossification a 

 second region (&), in which clear and remarkably large cells 

 containing beautiful spherical nuclei are found. The larger 

 size of these cells, in comparison with those contained in the 

 region just described, is to be attributed chiefly to the increase 

 of the diameter coinciding with the longitudinal axis of the 

 bone. This region contains in the same area a much smaller 

 number of cells than even the primary cartilage lying over the 

 region where they are arranged in vertical rows. Examined 

 with the naked eye, the region of large cells seen in longitudinal 

 section in fresh foetal bone appears clearer and more trans- 

 parent than any other part. This region presents a great 

 similarity to that stage of foetal cartilage in which the cells 

 are still capable of being easily isolated. 



Between the large transparent cells such strong trabeculse of 

 the matrix alone intervene as run parallel to the longitudinal 

 direction of the bone, and between which the cells lie in single 

 or more frequently in multiple rows. Where these trabeculse 



Aeby, Zeitschrift fur rationelle Medicin, 3 R., Band iv., p. 38, u. d. f. 



