The structure indicated is the outer longitudinal muscle layer of the stomach.

The stomach walls consists of four parts:

• Mucosa
• Submucosa
• Muscularis externa
• Serosa

The muscularis externa is the muscular layer of the gastrointestinal wall. In the stomach it consists of three layers:

• Inner oblique layer
• Middle circular layer
• Outer longitudinal layer

Between the middle circular layer and outer longitudinal muscular layer lies Auerbach’s plexus (the myenteric plexus).

Learn more about the digestive system in this tutorial