The illustration above shows the principal landmarks on the rat skull. Bregma is the landmark most commonly used as a reference point for stereotaxic surgery. Lambda has been used as a reference point but is chiefly used to align the rat head into the skull flat orientation
Note that the position of Lambda is not precisely at the intersection of the skull sutures, but rather positioned on the curve of best fit, where God should have placed it.
The sutures on the rat skull are often more irregularly organized than those shown in the illustration. You may have to use your judgement to select an appropriate approximation of the ideal bregma or lambda. Make sure that your selections are located on the midline.