54 



NORMAL HISTOLOGY. 



Periosteal Bone. Simultaneously with the formation of the 

 central spongy.,endochondral bone the cells of the osteogenetic layer 

 of the periosteum are actively engaged in likewise producing osseous 



tissue, the trabeculae of which unite 

 FIG. 62. to form the peripheral net-work of 



periosteal bone, this in many 



FIG. 63. 



Developing bone trabecula of endocbondral 

 bone : a, the new bone ; b, bone-cells ; c, still 

 unabsorbed remains of calcified cartilage-matrix. 



Developing bone the surface of portion of 

 bone-trabecula, exhibiting the conversion of the 

 osteoblasts into the bone-corpuscles : b, lacuna 

 with young bone-cell ; o, osteoblasts arranged on 

 the surface of the newly-formed osseous matrix 

 (;) ; at / an osteoblast just being isolated. 



places forming an outer envelope closely embracing the central endo- 

 chondral bone. 



The details of the process by which the osteoblasts are converted 

 into the bone-cells are the same in both the intracartilaginous and 

 the periosteal formation. The bone-matrix, deposited through the 

 agency of the cells, gradually accumulates around the osteoblast, until 

 this lies completely surrounded by the young matrix, when, after its 

 isolation from the marrow-cavity, it becomes the bone-corpuscle. 

 At first the canaliculi are wanting, as are, also, calcareous matters ; 

 these later appear. 



The conversion of the original spongy into compact bone 

 depends upon the development of additional lamellae within the 

 meshes of the primary osseous net-work. As an initial step, a local 

 absorption takes place, resulting in the enlargement of the pri- 

 mary medullary spaces contained between the trabeculae of the 

 periosteal net-work ; these osseous bands are thus reduced to thin 

 bony partitions between large oval cavities, the Haversian spaces. 

 A new growth of bone subsequently takes place within these spaces, 



