Abstract
The cephalic aorta of Octopus vulgaris has a fairly complete endothelium lining the lumen, a thick complete basement membrane, a layer of circularly orientated and a layer of longitudinally orientated muscle fibres. Presumptive synaptic endings are of two types. In the circular muscle, axons containing vesicles, contact club-shaped projections of the muscle. The gap between the pre- and postsynaptic membranes is less than 100 A and in some places apparently forms a “tight junction”. The second type of ending has been found in the longitudinal muscle; here axons full of vesicles end on the muscle. The ending is enclosed by a “mesaxon” of muscle and the synaptic gap is approximately 100 A. In the smaller blood vessels, axons end on myofilament-containing pericytes of blood vessels (equivalent to small arterioles). The endings contain vesicles and have a synaptic gap of 100 A. Only some of the pericytes seem to be innervated and transmission between one pericyte to another may be mediated by specialized junctions between the cells. The smaller non-myofilament containing vessels (equivalent to capillaries) are not thought to be innervated.
Published Version
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