Final answer:
The medial border of the inguinal triangle is formed by the edge of the rectus abdominis muscle, with the region being clinically significant for the occurrence of direct inguinal hernias.
Step-by-step explanation:
The medial border of the inguinal triangle is formed by the edge of the rectus abdominis muscle. The inguinal triangle, which is a concept in anatomy also known as Hesselbach's triangle, is defined by three anatomical structures:
the inguinal ligament forms the base or inferior border, the lateral border is formed by the inferior epigastric vessels, and the medial border is constituted by the lateral edge of the rectus abdominis muscle. This region is of clinical significance as it is the site through which direct inguinal hernias protrude.