As an item in the comparative anatomy of vertebrae, the occurrence of the splitting lines of vertebral bones was studied on the rabbit, the eared seal, the dog, and the domestic fowl, and the changes thereof taking place in the course of development of the vertebral bones were also studied using the dog as experimental animal. The material were routinely decalcified with 5% HCL solution, then punctured with needle which been previously immersed in China ink. These were then fixed and preserved in 70% alcohol. It was summarized that the splitting lines of the vertebral bones were to be classified into the line system and the irregular lines, and the former served to show the developmental architecture of the bone's superficial layer, revealing sometimes even the ecology of the animal concerned. The irregular lines, however, were nothing but the manifestation of disturbed growth orientation of the bone to be interpeted as defensive response of the bone against various extrinsic forces including physiological muscle exerrion, and this would be called the direct proof of the function exerted by the vertebral bone itself.
