part of part of embryonic structure bulbus cordis conotruncus rostral half of bulbus cordis bulbus cordis rostral half cardiac conotruncus The distal portion of Bulbus cordis that forms an outflow channel and gives rise to the proximal conus cordis. VHOG:0000437 EMAPA:16338 The conus arteriosus is considered a component part of the heart because it has a myocardial wall and lies within the pericardial cavity. It is a feature of the evolutionary primitive state. In amphibians it is called the bulbus cordis, a term that is also used for its equivalent in mammalian embryos. The more derived extant bony fish, like the zebrafish, do not have this cardiac compartment. They have a so-called bulbus arteriosus, which is not enclosed by cardiac muscle, but by elastic tissue and smooth muscle, and therefore is considered to be a specialization of the proximal part of the ventral aorta (256). However, similar to the mammalian condition (306, 326, 339), the bulbus arteriosus in zebrafish embryonic hearts is surrounded by myocardium that disappears with development (134, 135). The bony fish bulbus arteriosus might thus be homologous to the shark conus arteriosus and amphibian/mammalian bulbus cordis.[well established][VHOG] UBERON:0006060