On a Non-striped Muscle of the Orbit, 323 
fibrous membrane which completes the cavity of the orbit as 
entirely composed of white inextensile fibres. Gurlt* con- 
siders it to be a strong fibrous membrane, with yellow elastic 
fibres interpolated. H. Muller,t in a very brief communica- 
tion, states that he has found flat muscular fibres in the 
inferior orbital fissure in man, and corresponding structures 
connected to the membrana orbitalis of mammalia. 
It was supposed by those, who held that the membrana 
orbitalis was a highly elastic and not a muscular structure, 
that it was through its elastic recoil that the eye-ball was 
reprotruded in those animals which retracted the ball, 
through the contraction of a retractor muscle. H. Miiller, 
again, who speaks more positively than any who have pre- 
ceded him, not only of the existence of a muscle, but also 
of the kind of fibre of which it is composed, considers that 
it antagonises those muscles which retract the eye-ball into 
the socket, and that thus, the reprotrusion of the globe is 
produced, not by a mere elastic recoil but by a muscular 
contraction. 
If this hypothesis be correct, an arrangement exists in 
this locality which is certainly to be regarded as an unusual 
one, — viz., an involuntary muscle acting as a direct anta- 
gonist to a voluntary muscle. Whether the hypothesis be 
correct, or not, I am disposed to consider that the muscle 
has some especial relation to the vascular arrangements in 
the orbit. Its extension backwards to the foramina through 
which the orbital vessels proceed, and with which it is in 
immediate relation, and the very abundant vascular network 
found in connection with it, point, I think, to some special 
relation between the muscle and the vessels, a relation which 
is not at all inconsistent with what is known of the function 
of non-striped muscle in other localities. 
Note. — Since the above paper was in type, my attention 
has been directed, by Professor Huxley, to a communication 
by H. Miiller, dated Dec. 15th, 1860, entitled "On the 
Influence of the Sympathetic upon some Muscles, and on the 
Handbuch der Vergleich, Anat. der Haus. Saugetliiere, 1860, p. 733. 
t Siebold and Kolliker's Zeitsclirift, 1868, p. 541. 
