The area where the jejunum ends and the ileum part of the intestine begins. Although there is no clear distinct section, the ileum is narrower and has smaller villi than the jejunum. [ http://www.ncbi.nlm.nih.gov/pubmed/21802415 https://orcid.org/0000-0003-4183-8865 http://dx.doi.org/10.1016/B978-1-4377-2206-2.00068-3 ]