Excessive growth of nerve cells is a major feature of MEN2B.

Underneath mucous membranes like the lips and cheeks, nerve cells over-grow into little balls called "neuromas."

When nerve balls grow inside a lip, they enlarge the lip. Thus, people with MEN2B have large lips.

When a nerve ball is half-inside and half-outside of a lip, it produces a bump on the lip. (Think of an ice cube floating in water.) So, people with MEN2B have bumpy lips.

The photograph below was taken in 1865 (probably February):

Vertical arrows on the photograph show lumps, presumably caused by nerve balls that are half in and half out of the lips.

(There are better photographs, but this is the best one in the public domain.)

Photographs show that Lincoln had lumpy lips for at least 7 years. They also show lumpy lips in his sons Eddie, Willie, and Tad -- all of whom died before age 20.

The lips on Lincoln's son Robert are normal. He lived to 82.

An 1865 plaster cast of Lincoln's face shows more clearly the lumpiness of his lower lip.

The top photograph is from the Library of Congress. The bottom photograph shows the cast on display in the National Portrait Gallery in Washington, DC.