The influence of mercury chloride (HgCb) on development of nervous system (fore brain) of the chick (Gallus-gallus L. Var. Decalb) was carried out at Embriology Laboratory. Biology Department of Mathematics and Nature Science Faculty. Andalas University, Padang. Experiment method and Completely Randomized Design (CDR) with 10 replications were used. The treatment were 0.0 mg (K), 0.1 mg (1), 0.…