ANATOMY OF VERTEBRATES. 



23 



Vlv 



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

 communicate ; and they form the 14 



essential vehicle of the material 

 for future growth. 



12. Growth 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 f oruis assumed by the bone-cells in 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 Ions; bones in frogs, birds, and most of those in mam- 



O O 7 J 



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 



