Is a multi-tissue structure forming the smallest chamber of the maxillary barbel blood sinus. It projects into the barbel shaft and has a blood filled lumen, into which extend irregular septa of vascular smooth muscle cells. Additional smooth muscle cells surround the lumen and attach the bulb to the barbel core. Circumferential to the core, there is a thin band of dermal tissue through with run several smaller capillaries and the barbel branch of the of the facial nerve (cranial nerve VII). The entire structure is wrapped by a glandular, stratified epithelium. [ ORCiD:0000-0002-9900-7880 GOC:ymb http://zfin.org/ZDB-PUB-140813-6 ]