432 MOVEMENTS 



layer of fibrous tissue, but in some of the long bones two or three layers 

 may be demonstrated. This membrane adheres to the bone but can be 

 separated without much difficulty. It covers the bones completely, 

 except at the articular surfaces, where its place is supplied by carti- 

 laginous incrustation. It is composed mainly of ordinary fibrous tissue 

 with small elastic fibres, bloodvessels, nerves and a few adipose 

 vesicles. 



The arterial branches ramifying in the periosteum are quite abun- 

 dant, forming a close anastomosing plexus which sends small branches 

 into the bony substance. There is nothing peculiar in the arrangement 

 of the veins. The distribution of the veins in the bony substance itself 

 has been very little studied. 



The nerves of the periosteum are abundant and form in its sub- 

 stance quite a close plexus. 



The adipose tissue is variable in quantity. In some parts it forms 

 a continuous sheet, and in others the vesicles are scattered here and 

 there in the substance of the membrane. 



The importance of the periosteum to the nutrition and regeneration 

 of the bones is very great. Instances are on record where bones have 

 been removed, leaving the periosteum, and in which the entire bone has 

 been reproduced. The importance of the periosteum has been still 

 further illustrated by the experiments of Oilier and others, on trans- 

 plantation of this membrane in the different tissues of living animals, 

 which has been followed by the formation of bone in these situations. 



Physiological Anatomy of Cartilage. In this connection the struc- 

 ture of the articular cartilages presents the chief physiological interest. 

 The articular surfaces of all the bones are incrusted with a layer of 

 cartilage, varying in thickness between -^ and ^ of an inch (0.5 and 

 i millimeter). The cartilaginous substance is white, opaline and semi- 

 transparent when examined in thin sections. It is not covered with 

 a membrane, but in the non-articular cartilages it has an investment 

 analogous to the periosteum, called perichondrium. 



Examined in thin sections cartilage is found to consist of a homo- 

 geneous fundamental substance, marked with excavations called carti- 

 lage-cavities. The intervening substance has a peculiar organic con- 

 stituent called chondrin. The organic matter is united with a certain 

 proportion of inorganic salts. The fundamental substance is elastic 

 and resisting. The cartilages are closely united to the subjacent bony 

 tissue. The free articular surface has already been described in con- 

 nection with the synovial membranes. 



Cartilage-cavities. These cavities are rounded or ovoid, measuring 

 T2T7F to W of an inch ( 2O to 8o /*) m diameter. They are smaller in 



