Used in conjunction with a stereotaxic instrument (Models SR-5R/5M or SR-6R/6M) you already have, the Model SRS-A allows you to clamp the head of a knockout mouse or newborn rat and serves as a stereotaxic instrument. The SRS-A is configured so as to hold the tiny head of a small mouse or rat in position with its head clamp unit (mouthpiece and nosepiece) and auxiliary ear bars provided with fine adjustment functions. When used singly, it serves as a head holding device. The point of an auxiliary ear bar is available in varying sizes and easy to replace according to the intended use (e.g. to avoid the rupture of tympanic membrane or to fix the ears securely).