Development of the coronary arteries and cardiac veins in the dogfish (Scyliorhinus canicula).

The development of the coronary system in the Dogfish was studied using light microscopy. The sample examined consisted of 44 embryos and four newborns. The chronology of events occurring during the process was referred to the total length (TL) of the specimens. The nourishment of the developing myocardium first takes place by means of intertrabecular sinusoids. This system is later switched to a circulation through coronary vessels. The cardiac veins develop earlier than the coronary arteries. The earliest evidence of development of heart vessels in the present sample was the appearance of a diverticulum from the sinus venosus in three embryos of 31 mm TL. This diverticulum outlined the future coronary sinus. Both the atrioventricular and conoventricular venous rings were completely developed in an embryo of 36 mm TL. Coronary artery vessels appeared for the first time in embryos of 40 mm TL. In these specimens, two arteries arose from the midventral hypobranchial artery and divide to give rise to the four coronary artery conal trunks. In a 51-mm TL embryo it was already possible to follow the course of the coronary arteries, from the hypobranchial artery to the conoventricular groove. All main coronary vessels were fully developed in embryos of more than 58 mm TL. However, the arteries supplying the atrium were firstly recorded in a newborn of 77 mm TL. Birth usually occurs when the shark reaches about 72-76 mm TL.