Abstract
A description is presented about the arrangement of the whole vascular system and the lateral musculature of the yellowtail. The sino-atrial valves are bilaterally continuous with the longitudinal bundles of atrial trabeculae, which keep the valves closed during atrial systole. The afferent filament arteries leave the afferent arch artery rather oppositely, far from the filament rows to interlock with the basal portions of the efferent filament arteries, then run down towards the filaments. The departure of the coeliaco-mesenteric artery is preceded by baffles equipped within the median dorsal aorta, so that the straight aortic flow is partially turned towards the coeliaco-mesenteric artery. The segmental vessels are completely double-tracked, i.e., every unit consists of an artery and a vein closely coupling up to the distal end, instead of an artery or a vein alternating in a series. Such double tracking of the segmental vessels may represent a pre-adaptive modifi-cation that allowed tunas' ancestors to evolve the vascular heat exchangers. Each myomere is subsegmented into four “submyomeres” and as a result, the lateral musculature looks as if it were made up of a larger number of narrower myomeres.
