the widening continuation of the spinal cord, forming the lowest part of the brain and containing nerve centers that control breathing, circulation, etc.
See medulla oblongata in American Heritage Dictionary 4
(ŏbˌlông-gäˈtə)
nounpl.medulla ob·lon·ga·tas or me·dul·lae ob·lon·ga·tae(mĭ-dŭlˈē ŏbˌlông-gäˈtē)
The lowermost portion of the vertebrate brain, continuous with the spinal cord, responsible for the control of respiration, circulation, and certain other bodily functions.