The head is large and triangular, while the neck is greatly narrowed, almost one-third the width of the head. A pair of "horns" is present between the raised nostrils—tiny in "B. gabonica". The eyes are large and moveable, set well forward, and surrounded by 15–21 circumorbital scales. The species has 12–16 interocular scales across the top of the head. Four or five scale rows separate the suboculars and the supralabials, with 13–18 supralabials and 16–22 sublabials. The fangs may reach a length of , the longest of any venomous snake.