The fine distribution of blood vessels of the esophagus of rat, rabbit, and man was studied by the corrosion cast method. The vascular casts were made by injecting Mercox into the artery of the esophagus and removing the tissue with 20% KOH. These were observed under a scanning electron microscope. In addition, the healing process of an anastomosing part in the lower portion of the esophagus of rat was observed by the same method. In each layer of the esophagus particular microvascular patterns were observed as follows: 1) At the tunica adventitia thin capillaries formed a coarse meshwork, and large vessels ran through this capillary mesh in places. Capillary nets of muscle layers were thick and dense. These were composed of two layers which corresponded to the longitudinal and circular muscle layers. 2) Arteries of the submucosa ran longitudinally, and after branching or anastomosing, formed fine networks in the submucous layer. Numerous veins which pierced the muscularis mucosa from the lamina propria increased in diameter and also ran longitudinally in the submucous layer. They were connected by numerous cross anastomoses and some perforated the muscle coats of the esophagus to reach the outer surface. These vessels in the submucous layer constituted the submucous plexus. 3) At the lamina propria small arteries coming from the submucosa branched out and finally divided into capillaries. These capillaries formed a coarse and slightly elongated polygonal meshwork. In man the capillary mesh of the lamina propria projected into the lumen of the esophagus and showed a similar appearance to the vascular pattern of the villi of the small intestine. Small veins receiving their blood supply from the capillary mesh and connecting with numerous cross anastomoses ran longitudinally in the lamina propria and finally joined into the veins of the submucosa. 4) Microvascular patterns at each stage of the healing of an anastomosis of the esophagus were observed as follows. i) 3rd day postoperation: Vascular casts were lacking at the site of anastomosis. By observation with high magnification the buds of regenerating vessels were found at the wall of large vessels of the anastomosing site. ii) 5th day postoperation: The regenerating vessels had elongated, and anastomosis with vessels of the opposite side had begun. iii) 7th day postoperation: Revascularisation at the anastomosing part was
almost completed. The microvascular pattern of each layer still remained irregular and showed incompletion of the regeneration of blood vessels. iv) 14th day postoperation: As the constitution of blood vessels of each layer of the anastomosing part showed almost normal appearance it was assumed that the healing of an anastomosis of the esophagus had been mostly completed by this stage.