Fig. 1.

Illustration showing the in vitro brain stem preparation used in the present study. The preparation consists of only the pons with intact cranial nerves V through VIII. The cerebellum is removed. The drawing shows the pons dorsal-side up, viewing the 4th ventricle. The photograph shows a typical preparation ventral-side up, in which the abducens (VI) nerve is accessible for recording of reflex responses by a suction electrode (inset: anterior is downward). Stimulation of the trigeminal (V) and auditory nerves (posterior VIII) is also achieved with suction electrodes. Since turtles lack muscles of facial expression, nerve VII does not contribute to blinking.