Question: is the hippocampus part of the brain stem

Answer: No, The hippocampus (named after its resemblance to the seahorse, from the Greek ἱππόκαμπος, ``seahorse'' from ἵππος hippos, ``horse'' and κάμπος kampos, ``sea monster'') is a major component of the brains of humans and other vertebrates. Humans and other mammals have two hippocampi, one in each side of the brain. The hippocampus belongs to the limbic system and plays important roles in the consolidation of information from short-term memory to long-term memory, and in spatial memory that enables navigation. The hippocampus is located under the cerebral cortex (allocortical) and in primates in the medial temporal lobe. It contains two main interlocking parts: the hippocampus proper (also called Ammon's horn) and the dentate gyrus.