Chap, vii.] BONE* 55 



of varying length and thickness, and are composed of 

 lamellae of bone substance. 



According to the arrangement of the trabeculse, 

 the spongy substance is a uniform honey-combed sub- 

 stance, or appears longitudinally striated, as in the 

 end of the shaft. In the latter case the marrow spaces 

 are elongated and thetrabeculse more or less parallel, but 

 anastomosing with one another by transverse branches. 



68. Development of bone. Bone is developed 

 in the embryo, and continues to be formed also after 

 birth as long as bone grows, either in the cartilage, or 

 independently of this directly from the osteogenetic 

 layer of the periosteum. The former mode is called 

 endochondral, the latter periosteal, or intermembranous 

 formation. 



All bones of the limbs and of the vertebral 

 column, the sternum, and the ribs, and the bones 

 forming the base of the skull, are preformed in the 

 early embryo as solid hyaline cartilage, covered with a 

 membrane identical in structure and function with 

 the periosteum, which at a later period it becomes. The 

 tegmental bones of the skull, the bones of the face, 

 the lower jaw, except the angle, are not preformed at 

 all, only a membrane identical with the future perios- 

 teum being present, and underneath and from it the 

 bone is gradually being deposited. 



69. Endocnondral formation. The stage 

 next to the one (1) in which we have solid hyaline 

 cartilage covered with periosteum is the following 

 (2) : Starting from the " centre, or point, of ossifica- 

 tion," and proceeding in all directions, the cartilage 

 becomes permeated by numbers of channels (cartilage 

 channels) containing prolongations (periosteal processes 

 of Virchow) of the osteogenetic layer of the periosteum, 

 i.e., vessels and osteoblasts, or marrow cells. This is 

 the stage of the vascularisation of the cartilage. In 

 the next stage (3) the cartilage bordering on these 



