ANATOMY OF VERTEBRATES. 



23 



right angles in their course to the vascular canal, with which they 

 communicate ; and they form the 

 essential vehicle of the material 

 for future growth. 



14 





§ 12. Groivth of bone. — In 

 fishes the bones continue to grow 

 throughout life, and their peri- 

 phery, whether in the flat bones of 

 the head which overlap each other, 



Or in the thicker bones that inter- The forma assumed by the bone-cells iii man. cl. 



lock, is cartilaginous or membranous, and the seat of progres- 

 sive ossification. The long bones of most reptiles retain a layer 

 of ossifying cartilage beneath the terminal articular cartilage ; 

 and growth continues at their extremities while life endures. 



15 



Transverse section from the dense portion of the human femur, cl. 



Some of the long bones in frogs, birds, and most of those in mam- 

 mals, have their ends distinct from the body or shaft of the grow- 

 ing bone; these separately ossified ends are termed 'epiphyses': 

 the seat of the active growth of the shaft is in a cartilaginous 

 crust at the ends supporting the epiphyses. When these coalesce 

 with the shaft, growth in the direction of the bone's axis comes to 



