The guinea pig bile duct connects to the duodenum through a sphincter area, a terminal cavity and an ampulla.<BR>The evidence indicates that the bile duct proper extends only through the terminal cavity, while the ampulla is physiologically a part of the duodenum. Spontaneous electrical discharges of 15 to 25 per min. rise at the sphincter area and spread across the terminal cavity. They appear primarily along the surface of greater curveture of the cavity which also has the more highly developed portion of the nerve plexus. Simultaneous recordings of these discharges at several sites exhibit a phase delay from which a transmission velocity of 10 to 30 mm/sec can be culculated. The discharges which are observed as far as the end of the cavity abruptly end at that point and in most cases cannot be found in the ampulla. Further evidence of the separation is the fact that the ampulla contractions are coordinated with contractions of the duodenum. Weak duodenal contractions, such as pendulous movement, have no effect on the sphincter or terminal cavity discharges. However, large duodenual spikes do sometimes affect the bile duct discharges, but not in any systematic way, they sometimes inhibit and sometimes stimulate. In addition, the spontaneous sphincter discharges slow down and synchronize with the spike bursts associated with the duodenal slow wave whenever they occur.<BR>Histologically the ampulla has the longitudinal and circular muscle layers characteristic of intestinal wall. The terminal cavity has a similar double layer of muscle which becomes a single dense bundle at the sphincter. The common bile duct consists of a muscle fiber group with no distinct layers being apparent.<BR>The guinea pig bile duct follows a helical path just before it reaches the terminal cavity with the cavity itself at the apex of an acute angle bend into the ampulla. The terminal cavity is thus an active plenum having the sphincter at its input and a flap of muscle extending across the cavity-ampulla junction. The cavity along with this flap may act to control bile flow.<BR>Bile flows into the terminal cavity through the sphincter area. Then, bile is forced into the ampulla by contraction of the cavity. When the ampulla contracts in unison with the duodenum, it forces its load of bile into the intestine.