The muscular coat (muscular layer, muscular fibers, muscularis propria, muscularis externa) is a region of muscle in many organs in the vertebrate body, adjacent to the submucosa membrane. It is responsible for gut movement such as peristalsis.
It usually has two distinct layers of smooth muscle:
- inner and "circular"
- outer and "longitudinal"
However, there are some exceptions to this pattern.
- In the stomach and colon, there are three layers to the muscularis externa.
- In the upper esophagus, part of the externa is skeletal muscle, rather than smooth muscle.
The inner layer of the muscularis externa forms a sphincter at two locations of the alimentary canal:
- in the pyloric stomach, it forms the pyloric sphincter
- in the anal canal, it forms the anal sphincter
Read more about Muscular Layer: Additional Images
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