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 have written on the 

 structure of the orbital membrane, I find that the following 

 opinions have been expressed concerning it : — 



Bendz,f 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, which 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. J 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 effected 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. 

 ]N"ot 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 Arcliiv. 1841, p. 196. 



% Lehrbuch der vergleichenden Anatomie, 1846, p. 401. 

 \ Traite d'Anatomie Comparee, 1857, p. 753. 



