322 Proceedings of the Royal Physical Society. 
non-striped muscle, have I succeeded in obtaining more 
beautiful and more perfect specimens of the contractile 
fibre- cell than in this muscle of the orbital membrane. The 
fusiform shape of the cells, their size, and the elongated 
rod -like nucleus in the centre of each cell, gave to the tex- 
ture a most characteristic appearance. I may also mention, 
that when the orbital muscle in the sheep was examined 
without the addition of any re-agent, besides distilled water, 
a number of elongated rod-like nuclei were always met with, 
lying free in the water surrounding the preparation, which 
had evidently been loosened and detached during the dis- 
section with the needles. These nuclei corresponded in 
their characters to those met with in the interior of the 
fibre-cells. The characters which I have now enumerated 
render the muscular nature of the reddish texture connected 
with the orbital membrane sufficiently clear.* 
On referring to the authorities who liave written on the 
structure of the orbital membrane, I find that the following 
opinions have been expressed concerning it : — 
Bendzjf in a paper "On the Orbital Membrane in the Do- 
mestic Mammals," describes it as distinctly fibrous, but pos- 
sessing a considerable quantity of a yellowish tissue, w^hich he 
considers to be elastic, interpolated with it. He regards the 
opinion, which had been previously advanced by Gurlt, that 
the tissue was muscular, to be erroneous. % Stannius states 
that in those animals in which the bony wall of the orbit is 
incomplete, the separation between the orbital cavity and the 
temporal fossa is mostly efi'ected by a fibrous membrane 
containing also abundant elastic tissue. He states that 
Eudolphi regarded these elastic fibres to be muscular in 
Bears, and that Meckel described a muscle in the orbital 
membrane of Ornithorynchus. § Chauveau speaks of the 
* Since this paper was communicated, I have dissected the orbit of a red 
deer (C. elaphas), and found the orbital muscle very strongly developed in it. 
l^Tot merely did it constitute a large extent of the orbital periosteum, but it 
possessed a very decided reddish colour. In young human subjects I have also 
observed it very well marked. 
t Miiller's Archiv. 1841, p. 196. 
J Lehrbuch der vergleichenden ALnatomie, 1846, p. 401. 
2 Traite d'Anatomie Comparee, 1857, p. 763. 
