EPIPHYSIS PERIOSTEUM CARTILAGE. 29 



the apophyses, which are distinguished by anatomists by 

 names suggested by their position, by their use, or borrowed 

 from objects of which they recall more or less exactly the 

 form. 



The body of the long bones and the central part of the 

 large bones are developed % before the extremities and the 

 edges. The extremities of the long bones are cartilaginous 

 in early life, their articulating surfaces are formed of cartilage 

 adherent to, but not continuous with, the bone to which it 

 belongs. This is the epiphysis, which afterward becomes 

 ossified, but is not perfectly united to the bone till about the 

 age of twenty. Some of the large bones also present epiphyses 

 on their edges or borders. 



A white fibrous membrane, resistant in youth and reduced 

 to a thin layer of cellular tissue in the adult and aged, which 

 is called the periosteum, envelops every part of the bones, 

 except where they are covered with cartilage and where the 

 tendons and ligaments are attached. The periosteum adheres 

 closely to the bone, and distributes a network of vessels through 

 its substance. Recent surgical investigations have shown 

 that the periosteum plays an important part in the partial 

 reproduction of the bone after certain operations. 



Cartilage. To the bony system belong the cartilages, 

 which are formed of what might be termed tissue in a state 

 of transition between fibrous and bony substance. This 

 tissue, homogeneous in true cartilage, mingled with fibrous 

 substance in the fibre-cartilaginous parts, is elastic and flexible, 

 and in colour either yellowish or pearl-white. The cartilages 

 unite the bones at those points where, as in the chest, the 

 bony frame must yield to expansive movements; they furnish 

 a flexible skeleton to certain organs, as the external ear, for 

 example, the nose, the eyelids, and the larynx; and lastly, they 

 play an important part in the joints. 



No part of the organism shows more clearly than the bony 

 system the care which nature has taken to provide during 

 infancy the gifts of which she is so prodigal in maturity, and 

 which she withdraws little by little in old age. During in- 

 fancy, when protected by maternal care and when the growth 

 should be rapid, the gelatine predominates in the bones; 



