370 



SPECIAL HISTOLOGY. 



periosteal layers), — whether it be a kind of connective tissue, as 

 I believe, or a sort of cartilage, as Reichert and A. Bidder 

 assert, with respect to which more will be found in my 

 1 Mikroskop. Anat./ pp. 374, 375.] 



§ 107. 

 The secondary cranial bones, all, in the first instance, com- 

 mence in the form of a minute, elongated, or rounded, osseous 

 nucleus, consisting of a portion of fundamental substance 

 or matrix, with a few lacunae, and which is surrounded 

 by a small quantity of soft blastema. How this nucleus origi- 

 nates, has not yet been observed, although from the way in which 

 its growth proceeds, it might be assumed with certainty, that 

 shortly previous to its first appearance, a minute lamella of the 

 soft blastema is formed in the situation of the future nucleus, 

 which lamella spreading from a single point, becomes ossified 

 by the addition of earthy salts and the metamorphosis of its 

 cells. The primary point of ossification having thus appeared, 

 p- 135 for instance in the parietal 



bone, its growth advances 

 simultaneously with the hori- 

 zontal extension of the mem- 

 braniform blastema, in such 

 J£» j a way that a delicate lamina 

 YJh,^ composed of reticulated os- 

 seous spicules is shortly pro- 

 duced, from which, slender 

 rays stretch out into the still 

 X ./jOy i^v^v^Ai' unossified blastema (fig. 135). 



If this formation be ex- 

 amined more closelv, it will 

 be observed, that the indi- 

 vidual bone-spicules originate 

 in the membranous blastema, 

 by the ossification of its 

 elements, and, that to a cer- 

 tain extent, the latter is absorbed in the spaces occupied 

 by the spicules, remains of it being left in the interstices; 

 and moreover, that the formation of the osseous elements pro- 

 Fig. 135. Parietal bone of a fourteen-weeks old foetus, x 18 diam. 



