To better understand the function of extraocular muscles in birds of prey, we studied extraocular muscle architecture grossly and histologically.
This sample was composed of two each of th following species: red-tailed hawk (Buteo jamaicensis), Harris`s hawk (Parabuteo unicinctus), great horned owl (Bubo virginianus), and barn owl (Tyto alba).
All extraocular muscles were dissected and weighed.
To analyze muscle fiber architecture, the superior oblique and quadratus muscles were dissected, weighed, and sectioned at 5 μm thickness in the transverse plane.
We calculated the physiologic cross-sectional area and the ratio of muscle mass to predicted effective maximum tetanic tension.
Hawk and owl extraocular muscles exhibit significant physiological differences that play roles in ocular movements and closure of the nictitating membrane.
Owls, which do not exhibit extraocular movement, have muscle architecture suited to stabilize the position of a massive, tubular eye that protrudes significantly from the orbit.
Hawks, which have a more globose eye that is largely contained within the orbit, do not require as much muscular stability and instead have muscle architecture that facilitates rapid eye movement.
Source: Plochocki JH, Segev T, Grow W, Hall MI. Extraocular muscle architecture in hawks and owls. Vet Ophthalmol. 2018;00:1–6. https://doi.org/10.1111/vop.12553
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