Eyelids and Lachrymal Apparatus of Birds 
13 
attached to an apophysis of the bony circle) and reaches the pos- 
terior-inferior angle of the third eyelid, to which it is joined and 
of which it formed an integral part. 
At this point the (flat) tendon of the pyramidalis lies in a 
groove — almost a tube — on the eyeball. It now enters behind the 
conjunctiva, pierces the lower sac at a point slightly posterior to 
the median plane of the eye, and is attached mostly along the free 
border of the third lid, as a rope is bound to a sail. The fibres of 
the tendon are, some of them, also spread out fan-like and are lost 
in the tissues of the nictitating membrane. 
As the posterior-superior attachment of the third lid to the globe 
is posterior to the vertical plane and well up in the superior cul-de- 
Fig. 7 — Posterior View of the Left Eye of the Sparrow Showing Ar- 
rangement of Muscles and Glands, x 8. (Wood and Slonaker.) 
L, Lachrymal gland; h, Harderian gland; re, rectus externus; ri, rec- 
tus internus; r inf, rectus inferior; rs, rectus superior; oi, obliques inferior; 
os, obliques superior; q, quadratus; t, tendon from pyramidalis muscle to 
nictitating membrane; op, optic nerve. 
sac, it will be readily seen that the down-and-out pull of the tendon 
of the pyramidalis must cause the free border of the nictitating 
membrane to glide over the globe toward the posterior canthus. 
In ordinary contractions it seems to be drawn over to the sclera. 
Like the external rectus, the quadrate and pyramidal muscles are 
innervated by the sixth pair. 
Generally speaking, the oculomotor apparatus of Birds’ eyes is 
not endowed with great power and the movements of the eyeballs 
are much restricted. The protective muscular apparatus is, how- 
ever, highly developed. 
