

OSTEOLOGY ig 



forming cells. Its function is the same as that of the 

 periosteum. 



The Development of Bone. It is customary to 

 describe three varieties of bone development. These 

 are: "Intracartilaginous, intramembranous, and subperi- 

 osteal." It should be borre in mind, however, that the 

 essential nature of the process is the same in all. The 

 two latter are considered under one head. 



At an early period of life most of the long and irregular- 

 shaped bones in the body consist of masses of hyaline 

 cartilage, which present, in a general way, the shape of the 

 future bone. The transformation of these cartilage masses 

 into bone is intracartilaginous ossification. This is al- 

 ways associated with a certain amount of subperiosteal 

 ossification. The bones of the vertex of the skull and 

 those of the face, with few exceptions, are formed in mem- 

 brane; the base of the skull, the body, and the limbs are 

 formed in cartilage. In the former the bone-forming 

 cells (osteoblasts) arrange themselves along the thick 

 bundles of fibrous tissue which radiate from the center 

 of the future bone; by the deposit of lime-salts in these 

 osteoblasts bone-tissue grows out in needle-like rays to- 

 ward the circumference. A deposit of bone begins at one 

 spot in the cartilage and is termed the primary center. 

 The shaft is formed from this. Just before ossification 

 commences the cartilage cells enlarge and arrange them- 

 selves in rows. Lime-salts are deposited in the matrix 

 between the rows, forming columns which enclose oblong 

 spaces the primary areolae containing cartilage cells. 

 Ossification proper now commences by the ingrowth from 

 the periosteum of buds of young connective tissue, covered 

 with bone-forming cells, which, after causing absorption 

 of the cartilage, become converted into bone. 



