Which type of muscle makes up the muscularis in the lower third of the esophagus?

1. The muscularis of the esophagus changes composition along its length. 2. In the upper third it is skeletal muscle, which is why the start of swallowing is voluntary. 3. In the middle third it is a mixture of skeletal and smooth muscle. 4. In the lower third it is smooth muscle only, so control there is entirely involuntary. 5. Oblique muscle is the extra layer found in the stomach wall, not in the esophagus. _Source: OpenStax Anatomy and Physiology (CC BY 4.0), Ch 23 "The Digestive System", section 23.3 The Mouth, Pharynx, and Esophagus_