igO CHORDATE ANATOMY 



this way the marrow cavity of an adult bone becomes large enough to 

 contain the entire bone of the infant. 



The long bone grows in length at the two ends. Through endo- 

 chondral bone formation centers of ossification are formed within the 

 cartilage at the ends of the shaft. The bony centers are known as epiphy- 

 ses. During growth new bone is added between epiphysis and diaphysis in 

 a cartilaginous ''growth-disc." When adult size is attained the growth- 

 disc is converted into bone, the epiphyses fuse with the diaphysis, and 

 growth ceases. The regulation of size is influenced through the action of 

 endocrinal secretions of the pituitary and thyroid glands. 



