ENDOCARDIAL PORES IN THE SINUS VENOSUS AND ATRIUM OF THE DOGFISH

A scanning electron microscopy study showed the presence of large pore s in the endocardium of the sinus venosus of the dogfish Scyliorhinus canicula, The pores were always found on large bundles which protruded into the cardiac lumen. The bundles were mainly constituted of granul e-containing nerve fibres. The average diameter of the pores was 3.2 m u m (ranpe=1.5-5.0 mu m), and their density, was about 822 pores mm(-2 ). Endocardial ports were absent in other areas of the sinus venosus, but they were observed on the little bundles of granulated nerve fibre s which were scattered throughout the atrium. The existence of large e ndocardial pores associated with bundles of granulated nerve fibres su pports the hypothesis for the neuroendocrine nature of the elasmobranc h sinus venosus wall. (C) 1995 The Fisheries Society of the British Is les