THE OSSIFICATION SEQUENCES OF THE VERTEBRAL COLUMN IN THE CARP AND THE SNAKE-HEAD FISH

The ossification sequences of the vertebral column were observed in the carp and the snake-head fish. Features common to both species are: (1) Ossification of both centra and processes proceeded backwards as a rule. (2) A bone ossified later than both its anterior and posterior members in serial bones was assumed as being unable to reach the comparable size of the neighboring bones and as often developing into a modified form. (3) A few vertebrae just anterior to the urostyle ossified latest in the vertebral column, and often developed into modified forms. Characteristic differences between both species are: (1) In the carp, centra in most vertebrae ossified prior to the corresponding processes, while in the snake-head fish, processes ossified always prior to the corresponding centra. (2) Ossification of the 1st and 2nd vertebrae in the carp, i. e. precursors of the Weberian apparatus, was delayed for a short period, while such a delay was not seen in the snake-head fish. (3) In the carp, the urostyle was formed by fusion of a few separate bones, while in the snake-head fish it developed as one elongated bone from the beginning.