88 CONNECTIVE TISSUE CARTILAGE BONE 



In the flat bones of the skull, the central cancellous bone is designated 

 diploe, the peripheral compact bone, tables. Membrane bones may con- 

 tain typical Haversian systems (Arey, Anat. Rec., 17, 1, 1919). 



The conditions which determine that certain bones may arise directly 

 in mesenchyma while others must pass through a cartilaginous stage are 

 obscure. 



It is commonly believed that periosteum is essential for bone regenera- 

 tion, and its preservation is aimed at where new growth is desired after 

 osteotomy. But according to W. Macewen ("The Growth of Bone," 

 Maclehose & Sons, Glasgow, 1912), who has made a comprehensive ex- 

 perimental study of osteogenesis in regenerating bone in dogs, the perios- 

 teum functions simply as a confining, nutritive, and protective membrane, 

 but has no osteogenic significance. His observations lead him to conclude 

 also that in the long bones the osteoblasts are derived from proliferating 

 cartilage nuclei freed from the disappearing matrix. Under more favor- 

 able conditions regeneration is said to occur through direct osteoblastic 

 activity, under less favorable conditions a cartilaginous transition stage 

 intervenes. He deduces from his experiments that "diaphyseal bone is re- 

 produced by proliferation of osteoblasts derived from preexisting osseous 

 tissue, and that its regeneration takes place independently of the perios- 

 teum/' The periosteum is conceived as being an important factor in de- 

 termining the conformation and growth limit of bone. 



JOINTS 



Joints are divisible into two main types, the movable and the 'im- 

 movable/ or (1) diarthroses and (2) synarthroses. These and their 

 several modifications call for histologic description. Synarthroses include 



(a) syndesmoses, or joints in which the connecting substance is a dense 

 fibro-elastic tissue joining the bones immovably as in the articulation of 

 the skull (sutura), or where it consists of ligamentous tissue permitting 

 slight movement as between the lower ends of the tibia and fibula ; and 



(b) synchondroses, in which the connection is effected by cartilage, 

 either hyaline (e.g., between the epiphyses and diaphysis of young bones) 

 or fibrous (e.g., the inter vertebral disks of the vertebral column). 



In relation with diarthroses are in several instances (mandibular, 

 lower radio-ulnar, costosternal, sternoclavicular, acromioclavicular) 

 mtra-articular menisci of fibrocartilage ; here the articular cartilages of 

 the bones concerned are also of the fibrous variety. The semilunar car- 

 tilages of the knee and the glenoid cartilage of the shoulder joint are also 



