280 



ADAPTATIONS TO SPACE AND MOTION 



muscle thus represents the posterior portion of the ancestral reptilian 

 ciliary. Briicke's name is often applied to the whole of the ciliary in forms 

 below the birds, as well as to the radial or meridional portion of the 

 mammalian ciliary muscle where this has given rise (as in primates) to a 



/cm-. 



.pl/CP^ 



~-bm 



op 



^bp 



ch. 



-of 



Fig. 112 — The accommodatory apparatus of birds. Semi-diagrammatic; 

 based upon the situation in the hawks. 



ap- annular pad of lens; bm- Briicke's muscle; bp- base plate of ciliary body; c- cornea; 

 ch- chorioid; cm- Crampton's muscle (entirely intrascleral ) ; co- conjunctiva; cp- ciliary pro- 

 cess; i- 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; tcm- tendon of Crampton's muscle (continuous with inner layers of corneal sub- 

 stantia propria); tl- tenacular ligament; z- zonule. 



circular 'muscle of Miiller'. Quite another 'Miiller's muscle' occurs in 

 some birds, where it is simply the posterior portion of a further-sub- 

 divided Crampton's muscle, with its fibers still radial in orientation. In 

 lizards, Crampton's muscle is even more distinct from Briicke's than it is 



