8 bird's-eye views. 



muscles in a bird's eye as iu a mammal's. They are six in 

 number; whereof four are called "straight" muscles {recti) 

 and two "oblique" (obliqui) ; 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 iu from the brain ; and go 

 to be inserted into the eyeball at four nearly equidistant 

 points around its margin. One {muscuhts rectus superior, «, 

 in Fig. 1) goes to the top; another {m. r. inferior, c) to 

 the bottom, antagonizing the first ; the other two {m77i. r. 

 infernus, 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 

 {)n. ohliquus superior, e) going obliquely upward, the other 

 {m. 0. inferior, f), obliquely downward: they are inserted 

 near the margin of the globe, close by the insertions, res- 

 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 to 

 its insertion, whereas ip 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 cor- 

 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 eye 

 in difierent directions, and change the axis of vision ; and all 

 taken together, as stays to steady it. In tlie figure they are 

 cut away from their origins at the bony orbit, and reflected 

 away from the eyeball, to give a fair view of the pyramidalis 

 and quadratus. The reader must mentally collect the six 

 dangling ends, and fasten them in the places above desig- 

 nated. 



There are some other structures in the socket of the eye. 



