The orbital branches of the pterygopalatine ganglion and their relationship with internal carotid nerve branches in primates.

Details of the distribution and function ofnumerous groups ofautonomic nerves are still unknown; the rami orbitales or orbital branches of the pterygopalatine ganglion are among these. In man several rami orbitales issue from the dorsal surface of the pterygopalatine (sphenopalatine) ganglion and enter the orbit or the retro-orbital region through the inferior orbital fissure (Vitali, 1929; Andres & Kautzsky, 1955 and others). They have also been described in several animals (Ruskell, 1965). A clear concept of the distribution of the rami orbitales cannot be obtained from the literature. The results of many dissection studies and a few histological studies obtained over a period of 150 years are remarkably inconsistent and, probably as a result, interest in the rami orbitales has lapsed. Current reviews either overlook the rami orbitales or mention their presence without elaboration; only one review has been found which refers to their distribution (Duke-Elder & Wybar, 1961). Studies of the rami orbitales have provided little evidence of the identity of their nerve fibres or of their function. Muiller (1848) implied that the protrusion of the eyeball effected by contraction of the orbital muscle was mediated by sympathetic nerve fibres of the rami orbitales. Prevost (1868) considered that this was not the case because stimulation of the cervical sympathetic chain in dogs after extirpation of the pterygopalatine ganglion still resulted in protrusion of the eyeball. In the ensuing 100 years no further evidence of the presence or absence of sympathetic nerve fibres in the rami orbitales has been produced, and subsequent comment on the function of these nerves has been rare and usually speculative. Evidence that the rami orbitales contain parasympathetic nerve fibres was recently presented (Ruskell, 1965, 1968). Monkeys were used in the bulk of the work to be reported in this paper. The rami orbitales were examined by dissection, and electron microscopy was combined with conventional nerve degeneration techniques in order to determine the nature and the source of their nerve fibres. No adequate illustration of rami orbitales in man is available and therefore dissections of human material were undertaken for comparison with monkey material. One or more rami orbitales anastomose with the internal carotid plexus in man (Vitali, 1929; Andres & Kautzsky, 1955), and a para-abducens plexus of nerves derived from these two sources was described in rabbits (Ruskell, 1965). A similar