Which of the following terms means "inner region, medulla oblongata"?

The term that means "inner region, medulla oblongata" is medull/o. This prefix is derived from Latin, where "medulla" refers to the innermost part of an organ or structure. In the context of anatomy, specifically the nervous system, the medulla oblongata is the part of the brain located at the base of the brainstem that controls vital autonomic functions such as breathing, heart rate, and blood pressure.

In terms of medical terminology, understanding the roots and prefixes can provide clarity on the functions and locations of different body parts. Medull/o specifically highlights the inner region, which ties directly to its association with the medulla oblongata.

The other options do not relate to this concept. For example, medi/o often refers to the middle or central part of a structure, maxill/o pertains to the jawbone, and lymphaden/o refers to lymph nodes. Each of these has distinct anatomical meanings that do not align with the inner region context provided in the question. Hence, medull/o is the most appropriate choice for indicating the inner region of the medulla oblongata.