12 Casey A. Wood. 
found the quadrate muscle to be larger and better developed than 
the pyramidalis. 
The musculus quadratus is inserted into the sclerotic just behind 
the insertion of the rectus superior muscle. Its attachment fills in 
the space between the superior and internal recti muscles on the 
superior edge of the latter. From this insertion all its fibres are 
directed toward the optic nerve. The free extremity of the quad- 
rate muscle is about one-third as large as its size at insertion. Con- 
sequently it presents a triangle with a truncated apex rather than 
a square, as its name indicates. At this point, instead of having 
another insertion, fixed or mobile, the muscle abruptly ends in a 
tendon which folds on itself to form a fibrous loop, intended for the 
passage of the pyramidalis tendon. 
Fig. 6 — Posterior View of the Left Eye of the Sparrow with the Rectus 
Superior (Rs), Inferior (R inf), Externus (Re), Internus (R in), and the 
Superior (OS) and Inferior (Oi). Oblique muscles laid back to show the 
arrangement of the Quadratus (Q), Pyramidalis (P) and Tendon (T) in 
relation to the Optic Nerve (Op), x S. (Wood and Slonaker.) 
The pyramidal muscle, which is much smaller, is inserted under 
the anterior half of the inferior rectus muscle and on a line 3 or 4 
mm. in front of the edge of the muscle. It then reaches the ante- 
rior surface of the optic nerve and ends in a tendon which passes 
through the loop encircling the superior surface of the optic nerve, 
then enters a groove in the sclerotic, where it is held bv a contrac- 
tion of the capsule of Tenon. It then passes from within out, be- 
tween the inferior and the posterior recti muscle — nearer to the 
latter — interrupts the bony circle about the nerve (in the Owl it is 
