In Petromyzon the visceral skeleton contains branchial basket. It lies external to the gill pouches. It shows 9 irregular vertical bars and 4 longitudinal bars on either side. The first vertical bar lies just behind the styloid cartilage. The second is in front of the first gill slit. The remaining seven vertical bars are behind the 7 gill slits. The last vertical bar Is joined to a cup like pericardial cartilage. It supports the posterior and lateral walls of the pericardium. The longitu1nal bars are called subchordal, epitrematic, hypotrematic and median ventral. The subchordal bar runs along the notochord. Ft is joined to the cranium In front. The epitrematic and hypotrematic bars lie above and below the gill slits. The median ventral bar is placed in the midventral line and partly fused with the corresponding bone of the other side.
In Petromyzon branchial basket give support to the gills. It will keep the gill slits open throughout.