THE AVIAN EYE 



645 



appears largely empty, but actually has a sinusoidal (lymph? venous?) 

 structure. Traversing this thick open layer, with their direction radial 

 with respect to the eyeball, there are connective-tissue cords and columns 

 which often contain (or consist largely of) muscle cells. These may be 



fC/Vs 



S0'~- 



^bm 



-bp 



ch. 



'•sr 



Fig. 191 — The ciliary region of a bird eye. 



(Semi-diagram of the temporal quadrant in the red-tailed hawk, Buleo h. borealis. Blood 

 vessels, including the canal of Schlemm, omitted). 



ap- annular pad or ringwulst of lens; bp- base-plate of ciliary body; c- cornea; ch- chorioid; 

 cm- Crampton's muscle; co- conjunctiva; cp- ciliary process; «- iris; lb- lens body; ot- ora 

 terminalis; pi- pectinate ligament; s, s- sclera; sc- scleral cartilage; so- scleral ossicle; so'- 

 overlapped portion of adjacent scleral ossicle; sr- sensory retina; icm- tendon of Crampton's 

 muscle; //- tenacular ligament; z- zonule. 



smooth or striated, and their contraction would obviously thin the chor- 

 ioid temporarily and draw the retina backward. In the flicker (and other 

 woodpeckers?) the chorioid is not empty-looking, but contains a thick 

 mass of mucoid tissue which has probably been developed to prevent 



