Is a multi-tissue structure that is located outside the maxillary barbel proper and is positioned on the lateral surface of the maxilla, medially attached to the lateral surface of the maxillary bone and is laterally is attached to a hemispheric capsule of dense connective tissue of the distal bulb. It connects with the smaller accessory chamber through a slight isthmus. It has a smooth muscle tunic from which extend luminally projecting muscular septa. [ GOC:ymb http://zfin.org/ZDB-PUB-140813-6 ORCiD:0000-0002-9900-7880 ]