
512 BIRD’S-EYE VIEWS. 
muscles in a bird’s eye as in a mammal’s._ They are six in 
number; whereof four are called “straight” muscles (recti) 
and two “oblique” (obligui); though for the matter of that, 
they are all of them straight enough. The terms refer to 
their line of traction. The four recti all arise near each other, 
at the back of the bony orbit, around the hole (foramen 
opticum) that lets the optic nerve in from the brain; and go 
to be inserted into the eyeball at four nearly equidistant 
points around its margin. One (musculus rectus superior, 4, 
in Fig. 1) goes to the top; another (m. r. inferior, c) to 
the bottom, antagonizing the first; the other two (mm. r. 
internus, d, and externus, b) respectively to the front and 
rear (or to what would be the inner and outer sides, if a bird’s 
eye were directed forwards like ours), and also antagonize 
each other. The two oblique muscles arise farther forward 
in the bony orbit, near each other, and then diverge, one 
(m. obliquus superior, e) going obliquely upward, the other 
(m. o. inferior, f), obliquely downward: they are inserted 
near the margin of the globe, close by the insertions, on 
pectively, of the upper and under recti muscles. Their action 
appears to be very limited: the most notable thing about 
them is that the superior one goes straight from its origin ” 
its insertion, whereas in mammals this muscle changes its 
direction almost at a right angle, by passing through a fibrous 
loop, forming a pulley, suspended from the inner upper or 
ner of the orbit, very much as the tendon of the pyramidalis 
changes its course by running through the sheath in the quad- 
ratus. The six muscles serve as so many ropes to pull the ey : 
in different directions, and change the axis of vision ; and a 
taken together, as stays to steady it. In the figure they are 
cut away from their origins at the bony orbit, and reflec : 
away from the eyeball, to give a fair view of the pyramies” 
and quadratus. The reader must mentally collect the si 
dangling ends, and fasten them in the places above desig- 
nated. 
i There are some other structures in the socket of the ey® 



