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The muscular layer (muscular coat, muscular fibers, muscularis propria, muscularis externa) is a region of muscle in many organs in the vertebrate body, adjacent to the submucosa. It is responsible for gut movement such as peristalsis. The Latin, tunica muscularis, may also be used.
It usually has two layers of smooth muscle:
- inner and "circular"
- outer and "longitudinal"
However, there are some exceptions to this pattern.
- In the stomach and large intestine, there are three layers to the muscularis externa.
- In the upper esophagus, part of the externa is skeletal muscle, rather than smooth muscle.
- In the vas deferens of the spermatic cord, there are three layers: inner longitudinal, middle circular, and outer longitudinal.
- In the ureter the smooth muscle orientation is opposite that of the GI tract. There is an inner longitudinal and an outer circular layer.
- in the pylorus of the stomach, it forms the pyloric sphincter
- in the anal canal, it forms the internal anal sphincter
- Muscularis externa of the colon - BioWeb at University of Wisconsin System
- Smooth muscle layers of the gut - BioWeb at University of Wisconsin System
- UIUC Histology Subject 23
- Histology image: 11601ooa – Histology Learning System at Boston University — "Muscle Tissue: smooth muscle, muscularis externa"