THE SUPPORTING TISSUES. 



101 



there are as many as eight different points at which the 

 process of ossification begins. 



Growth of Membrane Bones. The second class of bones 

 comprises the membrane bones. As previously stated, these 

 are bones which are never preceded by cartilage. A typi- 

 cal illustration of such a membrane bone is the parietal. 

 Preceding this bone in early life there is just an ordinary 

 connective tissue membrane, containing no mineral deposit 



Fig. 45. PART OF THE DEVELOPING PARIETAL BONE OF A FOETAL CAT. (After Schafer.) 

 sp, bony spicules, with some of the osteoblasts imbedded in them, producing the 

 lacunae; ost, osteoblasts partly imbedded in the newly formed bone; of, osteogenic fibres 

 prolonging the spicules, with osteoblasts between them and applied to them; a, granules 

 of calcareous deposit between the osteogenic fibres; at b the granules have become 

 blended, and the matrix is clearer; at c a continuity is established between the two adja- 

 cent spicules. 



of any kind. Portions of this membrane are still evident 

 on the skull of a new-born child, and are familiar as the 

 fontannelles. In the meshes of this membrane osteoblasts 

 find their way, which begin at once to secrete over it the 

 mineral matter of the bone. By this continued secretion of 



