Smooth Muscle of the Periorbita and the Mechanism of Exophthalmos

Abstract

DIscusSION on the mechanism of exophthalmos is rendered unnecessarily difficult by doubt as to whether the experimental results obtained on the dog and other mammals may properly be expected irn the case of human subjects. The work of MacCallum and Cornell (1904), Whitnall and Beattie (1933) and Code and Essex (1935) has shown that in the dog and cat exophthalmos may be produced by contraction of the periorbital membrane through stimulation of the cervical sympathetic nerve trunk at a point caudal to the superior cervical ganglion. To the smooth muscle of this membrane (or to the whole membrane) the name of M Muller's orbital muscle " has been applied (Muller 1858a, Whitnall 1932). The same name has also been given, by the same writers to a muscle in the inferior orbital fissure in man. In MIuller's article the muscles were said to be analogues. The human muscle has been illustrated by Whitnall. He points out that it cannot function like the muscle in lower animals owing to its different situation and size. The present writer has examined copyright.

Membranous Support for Eyes of Strepsirrhine Primates and Fruit Bats

“…The uniqueness of the PA from other fascial membranes in the region is well documented in the literature on mammalian eye anatomy, especially in regard to elastic and muscular properties (Brunton, ; Murphy et al, ). The confusion regarding its location and its distinction from periostea is likely partially because of the difficulty in dissecting this fine membrane and separating it from adjacent tissues.…”

“…d, b, c). Based on these components, which match descriptions of Brunton (), we identify this membrane as the PA. Anteriorly, the PA attaches to the tarsal plate (Figs. d, e).…”

“…The function of the PA as a muscular, elastic fascial sac, was conceptualized by Brunton () as a means to hold and orient the eyes anteriorly in dogs, and probably other carnivores. This would be critical for these predators, converging the right and left visual fields to increase depth perceptions.…”

“…These varied methods allowed us to identify unique characteristics of orbital connective tissues. For example, the PA is distinguished from other orbital fasciae by a combination of collagenous, elastic, and smooth muscle components (Brunton, ). The slides were studied using a Leica DMLB compound microscope at magnifications from x25 to X630.…”

“…In the dog and other mammals there is smooth muscle enmeshed within the PA (identified as a portion of orbitalis muscle, Murphy et al, ), encircling the eye. The tonus of this musculature acts to maintain the eye in its ectopic position (Brunton, ; Murphy et al, ).…”